The pack add features like extra building blocks to build everything you'd ever want to build, new mobs that you can tame or fight, a biomes mod that changes the appearance of the biomes while still maintaining the vanilla feel, a revamped nether and end dimension and a mod called Origins that will allow you to choose between different classes. Each class has its own perks and side effects.
But there is a catch. You only have 10 lives. If you die 10 times, you'll be banned just like in a normal hardcore world.