Since there Isn't a thread for Unleashed yet or otherwise similar thread.
I feel like unleashed is missing a few things in regards to what its predecessors had and more:
-Immibis Microblocks (Or any microblock mod really...)
-Jammy furniture (Or any furniture mod, this mod pack feels like it left a few holes in the decorative/fun blocks area, not to say the woodworker isn't fun but some of use like furniture, stone and microblocks)
-Chisel Mod (Adds in some easy to design cool looking pillars and other block structures out of materials like limestone and marble and many more)
-Galacticraft (if this or dimension doors ever become as stable as mystcraft it would be worth looking into, its hard to top a space station spawn point with a view of the entire planet below your feet on a multi-player server)
-Traincraft (Just tons of trainy goodness and sync's up nicely with railcraft, perfect for that subway station in between bases)
-Atomic Science/Mekanism (alright so I know these arn't exactly the most stable mods, atomic science might help interest those who have had to give up gregtech for this mod pack with its fission and fusion reactors and performance tweaks, and mekanism just has some interesting machines, though the universal cable will probably get banned on every server. Both of these mods in their current state are BC/IC2 compatible with fully modifiable configs to tweak energy conversion)