Just completed Splinter Cell: Double Agent (though it isn't technically a 'new' game). I thought it was good but I'm still gobsmacked that the developers have, after four attempts now, failed to iron out the kinks that have plagued the Splinter Cell series. From the sterile, crappy enemy AI to the pyro-effects straight from the PS2 and annoying first person view when holding a weapon, one would think that a platform as powerful as the 360 would support slicker, more innovative gameplay (which it clearly does with other titles).
I also finished Lost Planet: Extreme Conitions last night and while it was possibly the best looking game I've ever played (indeed the graphics blow even Gears of War out of the water) it left me strangely cold (excuse the pun). In addition to the visuals, the gameplay is enjoyable but the plot makes no sense whatsoever. Thus you are simply playing a series of levels and missions without any idea why and consequently it becomes quite boring about half way through. Oh and the final boss is ridiculously difficult to defeat.
Still, Halo 3 is out next month...