The only real accomplishments to do while playing this is level up your classes, once thats done theres literally nothing to do but the same cycle over and over again on the same maps with the same buggy ui monsters. 3/5 simply because of how long it lasts good otherwise.

Origanaly bought this game thinking it was a solo game, only to be dissapointed to find it was a co-op, well i thought what the hell, al have a go online since a bought it and cant send it back, absolutley brilliant, zombies , guts , weapons , what more could you ask for, i never thought co-ops were so much fun and this one is def a one to get, watch you team mates get attacked by 20 zombies and go to the rescue with a granade boom, top quality game ad def recomend for resedent evil fans etc , mind in the same breath dont buy it if you want to play solo, its not much fun after a week : )

This game, runs big fat zombie rings around L4D, the engine is better (Source = FAIL) the AI is better, the weapons, the perks, the achivements, the characters...the GAME is better.
6 player co-op is better than L4D's 4 player
fight zombies in hordes, not just all coming at you at once
Darker, more grungy feel to things
Based on the Unreal 3 engine, MUCH better than Source in every possible way.

Frequent Steam updates and a HUGE modding community offering "white-listed" maps (Maps that the developers have "adopted" and allow achivements and perks to be used on them) mods (including a L4Desq "versus" mode) called "mutators".

Cannot be beaten, except by Killing Floor 2...