The original PSP has a huge library of great games to suit all tastes, with CFW it's one of the best devices around. The latest CFW even lets you switch between custom and official firmwares hassle free. They're also pretty cheap, I picked mine up a bit over a year ago 2nd hand in perfect condition for $100.
I do find the little thumb stick really uncomfortable though, and it cramps my hand after about 20 minutes. But that's why I'm looking foward to the Vita, it has 2 sticks meaning action/shooter type games will be much easier to play, and they're actual sticks this time instead of little nub things like the current PSP has.
It also has some pretty nifty features like remote play. When I can't sleep I plug in the headphones, use remote play to turn on my PS3 down in the lounge and just chill in bed watching stuff on ABC's iview streamed via the PS3, all without waking the Mrs