If you want gruesome gory violence vs zombies, with lots of bloody and dismembered parts then this is the game for you. This is what I feel DI does really well. The basic combat mechanics against a couple of zombie types. The other stock gameplay features such as crafting, upgrading and maintaining weapons, character progression, inventory management, voice-overs, back-story - it does well too. These all add to the basic nuts and bolts of the game, making it a comparable experience than other games of its ilk.
However, all of this is cast aside by some really awful mistakes, that send the game down from what it could easily have been a 5 game.
The real villain of the piece is the terrible auto-save/checkpoint feature. This is broken to the point that you can lose over 1/2 hr of progress even if you think youre safe w/ the last checkpoint you managed to make. Weapons and artefacts you picked up or crafted can disappear. Your character can appear in a total different area of the map, even if you were nearer to another save-point.
Add to this the ridiculous decision made to have all items & creatures randomly respawn, periodically - probably for those playing in co-op more than anything and the gaming experience is nothing near what it should have been.
It would have been better if, for the single-player experience at least, the game map would not respawn too many items and certainly not all area's would respawn zombies.
Another issue is continuous quests & sub-quests you've managed to pick will not appear in your quest log when you load a saved game. You have to manually revisit every quest giver to get them back. Since you rely on the minimap to tell you where to go, and the minimap requires you to have a quest selected.... you are practically stuffed until you can find your way back to these NPCs.
This is about 2weeks in and there has still been no patch for the steam version to fix these issues.
You are also bound to find that once you get over 1/2 way in the game, combat become repetitive very, very quickly.
Co-op is fine while it lasts, especially given the nature of connecting for how long you want to and to whatever game you want. Though personally Ive had some issues staying in a game due to sound issues. But Im not sure if that was me or the game I was joining.
Other than that, the graphics engine is v. good, the combat exciting, the violence gory and the story and quests worth playing through - at least once. I doubt I will want to play past my first character though which is a shame, because I was really looking forward to smashing as many zombie heads I as I could before Rage comes out!