I have played this many times solitaire, twice co-op, and I love it. The game is oozing with theme and the struggle to survive the zombie onslaught is very intense, even on the lower levels. If you find the game too hard you can adjust the difficulty level.
The game offers simplified rules all the way to some fairly heavy game-play. At first I only tried the basic and level 1 rules, because even that was quite a bit to digest for a first game. Now I've added all the rules and I'm happy to say they add more strategic depth as well as Chrome/Narrative.
There is co-op play which I tried once with 4 players and once with 2. All of the information is open and most resources are shared. There is very little difference as to how the game works between solitaire and co-op.
The game also offers versus play, but I haven't even looked at the rules for that.
The one thing that drives me nuts about the game is the LUCK factor - the key actions and many character abilities rely on dice rolls. You could spend an action and accomplish nothing: no supplies gathered, no damage to the enemy, a special ability doesn't work, research isn't successful and so on. These all or nothing results can be a real game breaker if you have a series of bad rolls. I am thinking of developing a variant to help limit the luck factor, but, I'm not sure it's necessary. There is one character who greatly takes the luck out of the game if you use him and certain characters don't rely on luck for their key abilities.