Fantastic campaign, a bit short, but even better on co-op. I've played through it online two or three times, and once you've played it more than once it's easy to beat it in like 3-4 hours. And still fun.

One of my friends became addicted to it online and played it on my XBox far more than I did, so I have less opinion on the multiplayer. It was very fun, though, with a lot of glitches that Epic did a poor job of handling. Annex was definitely my favorite mode--it's fun to have a tactical game in which one death means you're out of the round, but playing with people you don't know generally inclines you not to want to talk to them, which kills off a vital part of making a team-based game like that work well.