I'm not sure where the 'story is bad' is coming from. Is it goofy? Yes. Is it build in an episodic structure? Yes. But those are intentional choices. It's about being a kid and juggling all these demands while still being the hero. The nature of the story is a perfect framework to explore that kind of world. I'm just not sure where the concrete examples of 'bad' are.
I think all the points have been stated, but it breaks down pretty easily:
1. Many of the games are scaled down ports that don't really take advantage of the benefits of a portable system. 2. Due to piracy or low attachment rate (or both) there haven't been a ton of original games developed for PSP (outside of Japan's monster hunter chaos) 3. High price of entry, especially with the PSPgo, an overpriced mismanaged fiasco of a product refresh. 4. The Nintendo DS exists, which is cheaper and has plenty more games along a wider variety of genres. It's also sold WAY more. I like my PSP a lot, but it's pretty easy to look at the libraries of the two portable systems and see why the PSP is firmly in second place.
@mau64: I'd also suggest shopping online if you can. You'll get better prices and you won't have to deal with the idiots who work at Best Buy. They will undoubtedly try to sell you something you don't want if you aren't entirely confident of what it is you're there for.
I would save up for that $170 card there, if I were you. I'm pretty sure Vista can run DX11, and you might as well get a GPU that has native support for it as well, just so you're not left unable to play something in a year that's DX11 only.