It's got to be Splinter Cell.
Hopefully it'll break my GTA addiction, which is why I've been rather absent from Live over the last few months! Well GTA and Halo, which I finally got round to playing in January.
Edit: Of course, thanks to the postal strike in Ireland, I'll have to pay full price at GAME, but that'll give me the opportunity to part X some rubbish (Star Wars Clone Wars and Bounty Hunter - don't ask).