I've played the kameo demo, its ok, everyone says its too short.
Perfect Dark Zero has good gameplay, the aiming is a bit hard, but you'll get use to it. The storyline is crap. Online is also great fun. I would recommend buying it, there's also onlnine co-op and the online is really fun, and the game feels like goldeneye. You can also have guests online.
PGR3 is a great racing, AMAZING graphics, but if you want more arcady, take NFSMW.
COD 2 (I dnt have it, but my friend does), is really fun, graphics are hood, its so intense and you feel like you're in war. Online is a bit laggy, and PDZ has better online and more variety.