I gotta say I'm really confused at the comments, and even the reviews of this game. It's actually a fun and simplistic strategy game. I've only played an hour of the single player mode, and really like it. It's basic rts, but rts nonetheless.
I think most people expected alien swarm with zombies, what they got was an rts with zombies. People complaining that the game is to slow, really need to re-evaluate what rts means. They can be fast games, but like this, they can also be slow.
Anyway, I bought a 4 pack in the hopes of playing coop, I will give it a go with friends once I unlock the coop mode, and try the levels again. Hell I might play it twice, in single player, because it's a very simple and enjoyable cheap title.
Too bad they patched their download version of the game on their website, and not the steam version, which is a disappointment