Everyone else is doing it. These are the ones I reckon it would be a shame not to experience.
DO NOT MISS

Batman: Arkham Asylum (PS3) – sublime action adventure; you genuinely get to feel like you ARE the batman as you swoop down on psychotic criminals from the shadows.

Shadow Complex (360) – surprisingly polished and addictive platform/2D combat/exploration fest. (And it’s going to be 800 MS confuso-dollars instead of 1200 in the next week or so.)

Flower (PS3) – Beautiful, serene, and satisfying… simply an amazing experience. Unique among games.

Assassin’s Creed 2 (360) – spectacular setting (renaissance Florence and Venice? Yes please!), beautiful to look at, fun to traverse, engaging story… sure, it could’ve lost the timed sections, fixed up Ezio’s habit of leaping off into space and implemented a better quick travel system, but it’s a first-class experience despite those faults.

‘Splosion Man (360) - silly but polished and satisfying platforming with an engagingly demented main character and ludicrous trial-and-error gameplay that remains fun no matter how many times you rocket across the screen and plunge to a splodey death.

Uncharted 2: Among Thieves (PS3) – Spectacular and the closest thing we’ve seen to an interactive movie since Half Life 2. (It’s not a patch on HL2, of course, but at least it pays attention to characterisation and knows how to make a linear experience feel epic.)
NOT QUITE THERE (BECAUSE THEY TOOK A GOOD THING AND STUFFED IT UP)
Modern Warfare 2 (360). Close, guys, but next time try
- a story that makes some sense (remember COD4?)
- multiplayer that’s not utterly broken for anyone not in the US (try a local filter).
Left 4 Dead 2 (360). Also close, but next time
- don’t COMPLETELY wuss out just because A Certain Country has an idiotic rating system. Release it in shops without the offending material if you must, but don’t prevent the people in that country from downloading the censored content and enjoying your game as it was intended.
- multiplayer that’s not utterly broken for anyone not in the US (try a local filter).
OKAY BUT YOU’RE NOT MISSING ALL THAT MUCH
Prototype (good/bad), Borderlands, Tom Clancy’s HAWX, Katamari Forever, Beatles Rock Band, Guitar Hero 5, Red Faction Guerilla (and its invisible walls).
What’re your picks? Have I left anything out I shouldn’t have?