I'm having a blast with Warzone Firefight! It is very difficult with random players though and I haven't played Halo since December so I don't have enough good REQ-cards. Three times I've managed to complete 5th wave. There also seems to be an annoying bug or something for waves in which you need to kill 25 or 30 knights, they don't spawn quickly enough and it's a guaranteed loss.
Oh, if anyone here needs a code for 14 days of live gold, let me know. I think this code I found is still unused.