To start:

The basis of this new modpack is that you are no longer on the standard blockworld, but instead transported to a distant planet where the environment is hostile and the creatures are even more dangerous. Its made to increase the difficulty level of most packs and give you & your friends more adventure.

Many of the original biomes have been disabled, to provide a more hostile environment. The original/vanilla tools have been disabled, in favor of the newer Tinker's Tools. This forces you to properly level up tools/weapons thru mining and combat, in order to advance thru the game. Just like in the first mudpack, this was done to add more of an RPG feel, instead of just having to get 3 iron ingots, to mine all the materials in the game.

There are a ton of technology mods also added, which will offer many ways to generate power and run machines to further enable you to build more complex materials, machines and tools. And even ways to automate many processes and farming. (Big Reactors, Modular Powersuits, EnderIO, Gendustry, Thermal Expansion, Compact Storage, RFTools)

For those looking for a more mystical feel, many magic mods and add-ons have been included, to provide you with a different progression path, while also including new mystical mobs and bosses. (Botania, Thaumcraft, Tainted Magic, Soul Shards)

Even with all the technology and magic mods added in, there's still the additional mods (Foresty, Bibliocraft, Pams, Railcraft) to appeal to the the creative-builder players, to enhance their abilities to build breath-taking buildings and monuments.

Overall, this pack is great for single players and just as great for multiplayer server communities, as long as you understand the dangers around every corner and don't mind a little more challenge than traditional modpacks offer.

CritPack 2.0 - CritWorld