While not an RTS or FPS, this is pretty much amazing in coop. The closest I can peg it down is an action RPG like Diablo, except it's almost pure mix and match spellcasting, with horrific amounts of accidental friendly fire. It's hilarious.
It's still slightly buggy. Over 6-8 hours of playtime in online coop, I've had one CTD, and a few issues (people turning invisible, people getting stuck, etc) that required a restart/rehost. Also, controls take some getting used to, and you need to experiment to figure out some of the basic spells.
But heck, you can currently get a four-pack for 15$, I think. Or, you can get 2 of the complete pack with the new Vietnam expansion for 16$.
Still, casting thunderbolt like mad only to realize that you've just turned all 3 of your buddies into piles of bloody giblets is totally worth it.
Disclaimer: I haven't tried this without a net connection, so I can't verify that it works over LAN. However, the online connection mechanism has a LAN filter, so I assume that it supports it. I'm kind of assuming that even if you don't have net locally, you can download games somewhere?
