This mod has more content in later versions, I will cover all illagers added until 1.18.2 the latest version of the mod currently, even if I mostly played with this mod in 1.12

What is it ?

A mod adding new illagers to the game, alongside a few structures to incorporate them. Later, after 1.14 dropped, they eventually added these mobs as raiders to encounter as well as new illagers with this vanilla mechanic in mind.

What does it offer ?

New creatures for the illager group as well as new structures to make their presence unavoidable within your Minecraft world; this mod also features some customized potions to pick up in some structures as well as a new enchantment to deal more damage to illagers (the same found in Minecraft Dungeons).
Every mob added by the mob is tied to the illagers, list below :

Here's the whole list of Illagers (SPOILERS) :

Present since 1.12

-The Archer :
A concept of an archer illager it nothing new, even in 1.12 as the hunter illager mod also featured a bow-wielding illager. This one is still a bit more interesting than just being a skeleton which can survive daylight as in 1.12 it is a ranged vindicator, which means it is significantly faster in its movement; In recent versions, the archer received its own more unique texture and is no longer as fast, firing arrows with random potion effects. Even if I don't really like its textures, the detail of him having his bow on his back while not using it is something I love. (They have their own structure which is pretty common, but might be seen often in other structures too) .
-The Enchanter :
Before Minecraft Dungeons was a thing, this mod added an enchanter : an member of the illager group all in blue playing on drums to give sudden boosts of strength to illagers nearby (while slowing you down too); He did not change from 1.12 to recent versions outside of receiving a skull mask on his face
-The Furantur :
A melee alchemist illager which will steal you potion effects if you get to close; sadly his behavior makes him interesting in situations so specific he ends up boring in many. He is not that great unfortunately
-The Hoarder :
Reminding me a bit of the behavior of the maid illager from the more recent mod Belly Button, this mob will look for items left on the ground and take them with him, dropping them on death. Main difference between his 1.12 and recent version is the fact that in 1.12 this mob didn't have any sound effects (reusing the player hit sound effects instead of illager sound effects). I feel like he is a bit too specific in his behavior to be well used in most scenarios he is put in, his main purpose I would guess is to steal the player's drops after which death within a larger structure like the illager fort, making him able to keep them from disappearing since he will carry them on himself instead
-The Necromancer :
An evoker variant which will only summon zombies and defend himself with several rows of fangs (he also tries to attack with the same defensive attack, which leads to him using a spell which cannot reach his enemies, slight oversight which could be corrected); there isn't much to add, but I find him to be one of the few good enough necromancer concepts portrayed as an illager (better ideas exist, especially within undeads, but among illager mods there's a surprising lack of decent necromancer concepts)
-The Illager King :
Just a more resilient, taller and stronger vindicator; he is used as a form of final miniboss within the rarest structure in the 1.12 version of the mod (at least), and outside of that serves little to no purpose of his own

Post 1.12 Additions

-The Berserker :
Probably designed and intended for raids at first, this mob looks like a gilded pillager with his face being taken from the raid omen potion effect. He is a melee illager which can grief certain blocks in order to reach his target
-The Illager Miner :
Having his own dedicated structure, the miner is more interesting than the excavator from Workshops of doom as he isn't just a less powerful vindicator but has abilities of his own involving explosives
-The Frostmancer :
Having his own structure, the clear parallel to the iceologer that is the frostmancer (that is, if he wasn't added beforehand); He has about three attacks with a blizzard area effect, frozen falling stalactites or summoning a stalagmite from below his target. I find him a bit too aggressive at times, but still a decent mob.
-The Illager General :
In raids, this mob generates small pillars with pillagers on top acting as proximity turrets, a concept reminding me of the Modifiger mod; I don't really like that he has no animation at all when attacking in melee though

-The Black Iron Golem :
The illager equivalent to the iron golem, this mob can also shoot explosive fireballs; I don't really like that he can deal melee damage without there being an attacking animation at the same time

The structures added (some on screens shown) are larger in 1.18 than in 1.12, and newer structures have been added, most notably the fort, but also other structures tied to newer mobs from the mod.

For the critics :
First of all there is no unique sound to discern one illager from another as they all reuse vindicator, pillager, evoker and illusioner sound effects.
All structures aren't particularly exceptional, mostly being an excuse to bundle the mod's illagers together (even more noticeable with some larger structures, such as the 1.18 illager center where hoarders and enchanters are pretty much everywhere), I usually don't take the time to really consider structures for mods like these but since some are actually larger dungeons I felt like I had to mention that.
In recent versions I noticed some structures appearing above water in oceanic biomes (the frozen castle appeared once or twice above water for some weird reason).
Most of the mobs while having received already a texture update could still benefit from another facelift as they appear pretty bland in comparison to many other modded raiders out there (aka in 1.12 it could have passed but no longer does in recent versions).

In conclusion

While a lot of mods have a similar level of quality (it being "good enough" in terms of gameplay and not that interesting in terms of aesthetics) in recent versions, it's hard to come across one with so many illagers added in 1.12 and so this mod ended up being used a lot in packs which wished to feature more illagers while sticking to that version of the game.
I would like to point out that I've seen textures packs reworking this mod's textures somewhere on modrinth, it is probably worth taking a look if you plan on using this mod seriously.

It is not an amazing illagers mod, and in comparison to some made in recent versions (Goety, Illage and Spillage, Illager Additions...) I would say it is really not that good, but it has some good ideas which could be exploited in interesting ways by other modders I'm sure.