I didn't like the psp because it was too large and had a umd drive. I wanted something that was more of a handheld device, something that actually could fit in your pocket and something that you didn't need to bring hard copies of your games around with it. But as a mini-ps2 it's awesome.
I've played the psp, and loved it. God of War is incredible on it, so is burnout, very addictive. Even loco roco.
But I love the idea of the psp go, smaller, lighter and no UMD drive. Sadly it is horribly overpriced. They mixed up the old slogan "More for less" and got it backwards.