$350 entry price plus $250 XBL Gold are the main reasons. On top of all that, the two exclusives that I'm most interested in are barely exclusives anymore; Bioshock is coming soon, and at the very least I'll be able to play Mass Effect 2 sometime down the road with the possibility of seeing ME 1 also.
The RPGs are intriguing, especially Eternal Sonata and Lost Odyssey, but I never really got into Star Ocean (PS) or Star Ocean (PS2) or Tales of Symphonia (GC) even though I gave the games plenty of time to grow on me (I played 'em for more than 10 hours each). I'm a big FF and Suikoden fan and I have plenty of RPGs on my PSP and PS2. Fable 2 sounds great too, but I still haven't played my copy of Fable 1 on Xbox.
My Top 5:
Shadow of the Colossus, Metal Gear Solid 3, Shenmue, Skies of Arcadia, Chrono Trigger
My 2 nex-gen systems: PS3 
and Wii 
Prediction Aug '08: We see the PSP2 released fall '09. Graphically, it's basically the same as the current system. UMD drive ditched and replaced by 4-8gb on board flash memory. Other upgrades: 2nd analog nub, touchscreen, blutooth, motion sensor. Design: Flip-style or slider. Size: Think Iphone. Cost: $199. Will be profitable on day 1.
