It's kind of blah as an emulation machine. Except for PS1, that's pretty good. I think they did some fancy stuff with the hardware due to the CPU simularities, i've heard it called "simulation" instead of "emulation" for PS1. PSP games are pretty sweet when you run them from a memory card instead of the big disc drive, which fixes my original complaint about the system when it was first released. There's a pretty widely disseminated REDUMP set out there on some DDL sites and some good torrents.
One thing I haven't seen mentioned much online is that PSP systems do not seem very tolerant of large microSD cards. Compatibility can vary based on the exact microSD->sony bullshit adapter used. I tried to use a 200 GB card but couldn't get the PSP to actually format it correctly, so I went to 128 GB. The 128 GB card works, but there are predictable, relatively long (2-3 second) pauses at times when the card is accessed, such as when calling up the games list on a fresh boot. This effect seems to depend purely on the size of the formatted partition, and not on how full the partition is.