So after having played a modpack with Abyssalcraft on it, I found myself spending most of my time using Abyssalcraft exclusively. I love this mod and I think it has a lot of potential, but I came across a few major problems that make the mod worse than it could have been

Warning: This post is pretty long

1. The mod is very self contained
This isn't inherently a problem if it's done right, but I feel it's something that Abyssalcraft suffers from. There's very little items/concepts included in the mod that have any real impact on Minecraft outside Abyssalcraft itself. After beating J'zahar, the final boss, I was left with a feeling of completion but not really a sense of satisfaction, as if nothing I'd done up to that point mattered any more. I got J'zahar's staff and the Abyssalnomicon, but the mod had already been done, and I didn't have much of a reason to use these items any more, because they can only be used for mod relevant purposes.

My suggestion for this would be to add more items that have bearing on the real world. Things like spells/magic weapons/rituals that have an impact on more than just Abyssalcraft features

2. Balance
The enemies in Abyssalcraft all have significantly higher health than the default monsters, so understandably the gear in the mod is stronger to compensate. However, sets of armor like the Samurai armor and the Plated Coralium armor take a significant amount of work to make only a slightly stronger suit than diamond armor. I feel that the benefits the armor gives don't justify the vast amounts of work needed to get them

What I'd recommend is either buffing the armor sets, or making them more obtainable

3. Exploration
Abyssalcraft markets itself as an exploration/progression based mod, but I found that I had very little reason to explore overall outside the overworld. Dimensions like the Abyssal Wastelands and Omothol require exploration, but you're already told exactly where you need to go so there's no reason to deviate from that path. I never found myself needing to explore the other two dimensions at all to progress in the mod

My suggestion here is to flesh out the dimensions added to the game, possibly adding new structures or biomes, or adding necessary materials that require a bit of exploration to find

2. While the enemies are really difficult even with strong Abyssalcraft armor I fall that's appropriate given that these enemies are horrific monsters which shouldn't be trivialized. Having strong monsters even when using the best gear is very thematic for the mod.

I definetly agree with your 3rd point on exploration. The mobs and bosses added are amazing but the dimensions are very simplistic and do not seem to match the level of detail that the mobs do. Having to treck through the dimensions gets very boring aesthetic wise. Itd be fine if the dimensions consisted of one biome each but having them drag on in the same block doesnt meet expectation from the buildup to entering the dimensions. The mod is alot of fun otherwise :)