I got a chance to try out Firefall's unique blen of first-person, third-person, PvP, PvE, class-based, objective-focused Massively Multiplayer Online shooting at PAX Prime this year. I really, really liked what I saw. Of course, when you've got so many people playing together with different abilities and different enemies... it might be a good idea to keep it balanced.
I'm hoping GameRevolution nabs a bunch of beta keys for you readers to join the pre-release action. Let me know if you're interested in the comments.