The impact of this mod will be limited by the amount of advancement that need to do checks, which it optimizes.

If you have a cobbled-together modpack with something such as Blaze and Caves Advancement Pack, the performance hit is absolutely noticeable, opening chests takes visually longer, and this mod can turn this scenario into something stable. In this way it can be an obvious lifesaver.

It comes with a downside of that advancement triggers can be slower to trigger, and sometimes seemingly failing to trigger at all. This isn't that much of a problem unless its a complex trigger, and therefore advancement, not getting your fancy advancement sucks. This can also cause issues with mods that rely on advancements for progression gating, such as Spectrum and Pastel (and more specifically the APIs the rely on, Databank API and Revelationary API).

A useful performance mod, yet one with a gameplay impact. Rating it 3.5 of 5, has its obvious use cases. As a player or pack developer you should approach this as a case of cost/benefit.

"Survival Mode as it Should have Been" is a incredibly bold claim, a goal that they aim to reach and a goal they, in many ways achieve.

The number one differentiating of this mod compared to many others is that it rewrites survival, another way to think of it is that its nearly as if the developers use Minecraft as an engine to make a whole nother game. This and some similarities leads to a lot of Vintage Story comparisons. :P.

Gameplay

The mod makes the game have a much stronger survival focus, while Vanilla has you somewhat motivated by survival (building farms for food) its the core of the gameplay now:
Crops take ages to grow - you forage for food.
Food spoils - make vessels and use other methods of preserving food.
Need water - build infrastructure or settle near some water: so on and on and on.

The mod's progression in terms of tools is based around more and more complicated metalworking. Casting copper and bronze (which you alloy) by heating with a pit kiln, all the way until using charcoal forges and (oh dear, very expensive...) blast furnaces to make steel. TFC tool economy is very interesting, stone tools have very short lives, but by the time you get to wrought iron, you realize that these tools have netherite levels of durablity. Forging modifiers replace enchantments, casting gives none and your result of the forging minigame results in tools with what is equivalent to more unbreaking and efficiency to them. It makes the involved mechanics satisfying and to learn and master since you are getting such a good deal out of it!

Large and rock type dependent ore veins make exploration worthwhile, your single deep cave no longer contains everything you need. (sometimes annoyingly, your surface at world spawn may not even contain all you need to get into the copper age)

Worldgen

TFC's world generator is cell based, each containing a continent or ocean in its center, clmate changes as you go east-west (rainfall) and south-north (temperature) (btw it loops, like a triangle wave).

In 1.21.1 it is incredibly impressive, karst biomes at carbonic rock types, glaciers and drumlins at the arctic, mighty stratovolcanoes and shield volcanoes, and various types of coast line. Exploration always feels engaging as the world around you is molded by so many factors. Its hard to explain, just visit the gallery section on the mod page!

Mechanics

The mod has a myriad of mechanics, I don't know how feasible it is to name them, but I will pick a few.

Glassworking, introduced in v3 (for 1.20.1) it provides a engaging (and very laborious, something that really needs to be addressed) process to create jars, glass, and bits and bobs.

Lifecycle and calendar: crops and plants follow a lifecycle, gooseberries may only grow in early autumn, and crops only require the right climatic conditions creating a sense of seasonality in how you grow food. In the newest versions, tree leaves better react to the passage of time, flowering, falling and dis-coloring throughout the year visually showing the passage of time.

Metalworking, the item heating, anvilworking mechanics create value (and some tedium...) in what you make, as metal is scarce and may require reconsidering what you are making and how much. This can be boring and tedious at time and I recommend that players engage with this as far as they feel, no shame in never getting a bloomery and iron, if bronze is working perfectly fine for you.

Integration

The mod integrates itself into and expands on vanilla very well, adding somewhat location based rain, and tilt (which differs by time and latitude) to the sun and moon (yes, afaik eclipses are possible), some vanilla stuff is craftable and usable like armour trims (made through sewing now), tnt/gunpowder, beds (straw beds also let you set spawn point, but you cant sleep on straw beds), and bamboo.

its difficult to integrate with other mods, largely of tedium as so many things need edits but its generally possible.

Extendability

The mod has documentation in game and developer documentation online, its extensive use of data driven mechanics makes it possible and easy to create custom content using its existing mechanics, fostering a large culture of addons. In its code it makes good use of stuff like interfaces and events to allow for addons to make their own stuff like rock and wood types without too much hassle (except, block entities...)

Another cool thing for developers is its use of placed feature tags to make additions to worldgen very easy. (biome modifiers not needed!)

Notes

• Performance is surprisingly good for such a big mod, some places can suffer a bit like chunk generation speed, but comparatively to other mods there are much worse generation speeds than what TFC has.
• Its built-in textures can be a bit rough, a mixture of programmer art and modified modern MC art. Many people prefer to use resource packs such as Vexxed Visuals.
• I alluded to this, but there are a crazy amount of addons for this mod.

There is one thing which makes this stand out well, even when comparing against KJS: it has great documentation.

This contributes greatly to the developer experience of using this mod in your TFC modpacks. It provides builders for many TFC's blocks such as the plants and great utility features such as bindings for TFC classes, rock layer editing (I don't lean too hard on KJS, preferring Java and core mods for pack development, unless its the easiest option, and this frankly is the easiest way to add custom rock types.) and advanced features like "tree solving" (to create the nbt files TFC uses for trees in forests).

This is a one man project, there are typos, mistakes, and so on and generally the dev is accessible and kind when issues are reported to them.

Its inclusion of simpler features like ways to create TFC data and recipe types, makes it useful for users that are not knowledgeable in datapacks to be able to create stuff for their TFC modpacks.

Spectrum is characterised as much as by its content as by its journey. Its guidebook consists of a thought out, and commentary ridden step by step account of the journey the player takes. Its main reoccurring theme is the idea of revealing hidden things.

(it does so through revelationary API, which I note for modpack devs is data driven, though most of Spectrum's usage of it is in code, I haven't been brave enough yet to attempt to mixin this behavior to try to edit it).

Because of this, it would nearly be like spoilers to be specific, so ill try to be abstract with this review. Which might not work out as well as I want it to.

Your journey is characterized by puzzles and exploration, as you explore the world you "learn" more about it, this means you have a very continuous process of learning and applying your knowledge, and the discovery of these hidden things breaths life and intrigue into the overworld, nether (and not really the end, a bit though).

It has many unique mechanics, like potion effects, many, many tools and the structures you build (and are somewhat customisable) are reminiscent of the structure that magic mods like astral sorcery may have you build, serving a practical purpose. For a pack dev perspective, it has a lot of data driven recipe types which have potential to be used in creative ways.

Its art is nice, and this is true very consistently throughout the mod. Those storm stones look dangerous!!

Once you get to know the mod, the various steps can be a bit tedious though that's why this mod, no matter where you are or if you are a first time player or not, should be spaced out and not rushed, as you will get tired and frustrated (especially for the first time player!)

Also since I see performance as an optional rating, I just want to point out that in either Spectrum or Pastel (don't think this has been patched in either): don't place too, too, TOO much azurite, the particles can crash your game lmao. dont go crazy with the Create mod's worldshaper and you will be fine :P .

Starcatcher is an amazing mod adding a fishing minigame where a pointer revolves in circles, where you have to time it with sweet spots to advance the minigame. It has a large assortment of fish, and many different varieties on the minigame, where many fish especially the harder ones have unique challenges to catching them.

Something that is very welcome especially to mod/modpack developers like myself is data and registry driven design, making some base behaviours modifiable by any modpack dev. Nnew types of conditions, minigame modifiers and so on are simple enough to add through Java.

Its art is nice, can be a bit here or there I guess, though that may be a result of pulling art from various sources and artists.

It has many first party integrations with other mods such as Create (new fishes), and compatibility with fishes from other mods, and with mechanics like seasons from mods like TerraFirmaCraft. This means the mod can be drag and drop, though as the dev as said (afaik) these integrations are being thought over to make them better.

Modded biomes, since they currently rely on their common biome tags for compatibility, can be a bit barren especially in conditions like rain or ever just shine, and few fish types can be found in them.