It's pretty innovative but also somewhat gimmicky. Personally I quite enjoy it, it's not like Left for Dead where you HAVE to do this objective in THIS way or DIE. You can kinda forget around and get to the missions when you want to. Just make sure you have a good connection.
It's highly co-op based, you can play through the main story with other players to help you, or you can free roam, ect. My personal favorite is that someone can 'invade' your world as the super powerful night zombie and track you down, almost kinda like dark souls. At the end of the day you can change settings to get the online experience you want.