Honestly speaking, FTB StoneBlock 4 is a pack I didn't expect to like as much as I did. The original StoneBlock, released in 2018, was a novel idea and something of an unusual twist given the extreme saturation of the skyblock genre (no doubt exacerbated by the popularity of SkyFactory and Project Ozone). Since then, many packs have come out which use the same [something]Block formula, and a disappointingly large number of them are derivative. The same resource acquisition methods, the same rough progression, the same suite of popular mods, and a thematic coat of paint depending on the setting.
I mostly started playing StoneBlock 4 because it was a 1.21 pack that was relatively complete. While I thought the pack might be too directionless for me, its progression was pleasantly unexpected. The new methods of resource acquisition aren't too tedious (at least compared to the dreaded sieving) and somehow the pack manages to include exploration, a feat which saw me bored of digging tunnels and yet still enjoying every quick jaunt to a dungeon or hidden grotto. By far the most competent aspect of StoneBlock 4's progression is the way it branches, converges, and branches again in order to give the player multiple options but not force them to go too far down one path. One of the pack's various gimmicks is the World Engine, a stationary machine which is used for various crafts and which the player slowly upgrades as they progress. A World Engine upgrade or important craft acts more as a checklist of obtainable items which come from different mods; this allowed me to pick and choose the order in which I wanted to pursue the subcomponents of the next goal. This might not sound like much (and I can see someone who prefers linearity getting overwhelmed), but it's what kept me playing instead of being faced with the mandatory next task and just closing the game instead.
Speaking of overwhelm, though, this pack suffers from the same issue that plagues most large kitchen-sink packs: repeated content. Several mods are included that I barely, if ever, touched during my playthrough. Integration is minimal and often focused on the central progression; recipes which are not pursuant to a World Engine upgrade, for example, are usually untouched. For some reason AE2 and Refined Storage are both included, when I can't imagine a situation where I would use both. I pursued Malum, Ars Nouveau, and Occultism only because one item would be required for something else I was trying to do. I didn't even think about Hostile Neural Networks because Apotheosis spawners are exponentially more powerful. Mekanism and Oritech were my main technology(-themed) mods; Immersive Engineering seems like a formality. I'm not sure I ever actually used Create. Productive Metalworks is riddled with bugs and a very frustrating requirement; XyCraft is incomplete. The mod selection is somehow nearly the same as OceanBlock 2 despite the different locale, and this is where the earlier critique of similar packs with different aesthetics comes rushing back in full force. The parts of StoneBlock 4 I enjoyed most were those unique to the pack itself: the World Engine, the custom dungeons with compasses which lead you to them, the bespoke resource generation. There were some sticking points in the regular gameplay loop (I found the "events" so obnoxious I had them all turned off before I even had a proper base set up), but the quests felt mostly balanced with one another in terms of how much they asked the player to accomplish.
I would recommend StoneBlock 4 to someone looking for casual yet consistent modded experience on a newer Minecraft version. It's a fine pack for someone who enjoys automation, light exploration, and open-ended progression which doesn't expect the player to use every available mod.

Its okay, uses a custom map to its advantage and has innovative gameplay in the form of vaults, plus the quests are good and have decent explanations... but the lategame falls into the tediousness of ´go farm this very specific material, afk for 20 hours to get enough of it for one unlock, then go get a new mat.

Overall

It's a fun pack, play it!
I finished the pack solo in 75 hours, there is post-game content but I did not care for it.

What I liked

• The custom made "Vaults" were very fun to explore, except the maze which was broken for me
• A great introductory for newer mods (speaking as a 1.12 player) like Oritech and Just Dire Things
• I enjoyed the spawn area with the questline even though I didn't read any of the lore
• Early game is really fun and properly balanced with exploration and automation.
• The concept of the World Engine and the requirements to craft certain items

What I think could be improved

• Too many chickens! I ended up making them all because they're just by far the best way to generate resources
• The shops felt more like "we couldn't think of a good way to implement this so let's just make it a shop item"
• After the early game the pack didn't feel like "stoneblock" anymore, but just a kitchensink/tech/exploration pack which happened to be in a stone world. The different NPCs in the spawn area sell a certain item which makes it trivial to traverse to a certain "ring" in the world, and from there its just digging in a straight line where you want to go and thats it.
• The dungeons generating in each of the rings weren't worth it after early game
• Why was projectE in the pack? There were maybe 4 items with EMC, and the only other things you could make was the armor and the tools, but there are plenty other and more fun options.
• I wish it was easier to see what new recipes I could make after upgrading the world engine.
• In the final chapter you'll be working with mekanism a lot. Specifically reactors , nuclear waste and especially Antimatter . I really disliked this part, I made both the fission reactor and turbine almost as big as they go, and it still took multiple hours to get all the Antimatter needed to create a better way of obtaining it. I ended up cheating in 10 Antimatter for the Antimatter chicken purely because I had nothing else to do in the pack at this point and I did not feel like tripling my already big setup. Not to mention the power requirement to run the antimatter machine was leagues higher than everything else in the pack. I would've loved to see a different approach to this finale.

One of the first packs I've actually completed(although I'm not quite at the end lol, close enough!).
Unlike most similar packs there's no sieving or ex nihilo-esque stuff of any kind, there's a very unique early game that uses vanilla brushes, with a bit of villager slavery to automate it later.
The whole pack is centralized around crafting with and upgrading a device known as the World Engine. The texturing and theming for it is great, and it's not the most intuitive thing in the world at first but a very great questbook gives you enough to figure it out.
Speaking of, the questline feels great. It's got a sort of asymmetrical layout where you work on three different quest chains per chapter, and at the end of each questline is an upgrade for the World Engine(which unlocks new crafts to progress through whichever mods you want or need). Completing each quest gives a bit of money to purchase things at the spawn's shops. These shops are fully voice-acted characters which you talk to throughout the quests.
The quests are not fully exploration or crafting/techy stuff, I think there's a great balance. If you get bored of one or the other it's great to have two other quest chains to go through.
Mods are a nice mix of the ol' standards and some I hadn't really heard of until playing this pack. You've got your Mekanism, Ars, AE2, Apotheosis, etc.; Create is here but not super necessary like in SB3 or a lot of other packs, which is great. Two great mods that were new to me were Just Dire Things and Roost Ultimate.
Exploration is a mix of custom dungeons and bosses, mostly L_EC or Twilight Forest. The dungeons are all themed around one specific thing; there's a Create dungeon, a Portal dungeon, a puzzly MFFS(a forcefield mod) dungeon, etc. which are all very fun to go through.
Overall, progression never felt blocked in any way. It was like when going through a certain mod for the questline you'd watch a great cutscene as your World Engine grew and gain access to everything you'd need for that mod. The grind is minimal, and AE2 is very much buffed so once you get autocrafting it becomes even less tedious.

This pack's 100% worth playing, even if you're not a huge skyblock enjoyer I think it's worth it for the custom stuff alone.

it was a smooth steady gameplay for my friend and I, its a little rough early game. However, the "gambling" system makes it a little easier for early game, until mid game gets way easier and more enjoyable if you were to follow quests.

After around 80ish hours out into the pack, I can confidently say it is leagues above stoneblock 3. Where stoneblock 3 for example had quests which felt not that well put together, stoneblock 4 ended up being one of the best out together quest books with literal voice acting and lore!

The end game is satisfying. While there are technically creative items you can make after the end game, the story itself ends off at a good note with each upgrade of the world engine needing work done from different mods, all while progression gating some recipes depending on what world engine upgrades you have made. Quite a interesting way to gate progression in a well made way

This one was very competently done, with a skeleton story centred around upgrading "the World Engine". In practice that means working through different mods to create the necessary upgrades, and then watching the World Engine build itself in cutscenes.

Exploration
The world is made entirely of stone, so it's not one for sightseers. As you dig further out in the stoneblock world, you'll reach other dimensions. Teleportation mods make this less painful than it sounds, although some midgame quests require a lot of digging to find dungeons buried in the outer rings - there were slightly too many of those for my tastes.

The quest dungeons themselves are very well done, each centering around one mod in particular - e.g. Create, or Portal Gun. They often call on platforming abilities, and seemed of the perfect length.

Other more generic dungeons exist in each ring. These tend to be very rich on loot in the inner rings (the Nether dungeons in particular) and very loot poor beyond that.

The mod offering
There are a lot of mods in this pack, although quests do not force you through these. Many mods seem to be here to provide options - there are several storage mods, for example, and you'll only ever need one.

Particular focus is given to Oritech and Draconic Evolution, especially in the late game, although other technology focused mods include Industrial Foregoing, Mekanism, Create and Immersive Engineering. The magic mods in the pack (Occultism, Psi, Ars Nouveau, Malum and Iron's Spellbooks) are barely touched, although progression along Apotheosis' enchanting path is a core part of progression.

Resource generation is done firstly through villagers, and then through specialised cows and chickens - meaning that you'll never be short of resources. Although you may at times be short of the right chicken.

Pacing
Cataclysm and Twilight Forest bosses are in the pack. Some of the Cataclysm bosses appear first, and are much harder than the Twilight ones. The pacing is otherwise good, although the very late game really amps up the resource requirements (a collection of chickens is practically essential by this point). I did get bogged down with Industrial Foregoing's laser fluid drill, which gathers resources essential for progression incredibly slowly. It might be that there was a way to speed this up that I missed (that wasn't just craft two dozen identical complex machines), but it did mark the point at which I burned out, just before the end of the final act.

Summary
A world of stone might not be for everyone, but I would still personally recommend the first half of the pack. The quest dungeons are well put together, the generic dungeons are very rewarding, and progression flies along. Seeing the World Engine upgrade is a satisfying conclusion to each questline. The later half of the pack is more for the factory-minded, requiring a command of an array of tech mods, with magic by that point having been thoroughly sidelined. That half - while not for me - was nonetheless very well done, and there's a lot of joy to be found there by those with that kind of head.