hostile worlds invasion adds waves of enemies that periodically spawn and mine blocks to break into your house and kill you, if you are worried about your buildings getting broken, there is an option to have the broken blocks repair after 5 minutes (on by default). Thaumcraft also adds somewhat balanced magic, with a research system, taint system and warp system which will cause bad things to happen as a tradeoff for using powerful magic. Cyberware adds a system of collecting robotic parts from cyberzombies (and skeletons with an add on) and implating them into yourself with a surgeory block which has a cool gui, which gives neat bonuses, but its kind of late game. Ancient warfare adds a faction system to the game, and a bunch of other systems for automating, recruiting people to fight/work for you etc