I'd definitely say Splinter Cell, It's been an a very long time since one has come out so it should be amazing. It's a great game, and most of the people I know who don't like it are people you just can't be strategic and they just spray and pray through levels.
BioShock 2 will also be an amazing game to get as well, been waiting awhile for this as well after I had played it last year, but it's worthing waiting a bit longer after you play Splinter Cell.
Mass Effect 2 is the other game I also have been waiting for
I love BioWare games, and Mass Effect had a great story. Just hopefully they don't get lazy with using the same layout on all of the planets.