Amiga emulation on the PSP is pretty mediocre, in my opinion. Several of the games you mentioned has ST versions though, and you'll find that many of them play quite nicely.
Even better, the Genesis/Megadrive, SNES, or Playstation version of several of those games would be be more enjoyable, and you'll find the emulation to be near-flawless.
The custom chips and drive access routines make Amiga emulation on handhelds more of a novelty than anything else. There's just too much going on for something like the PSP, DS or iPhone to handle it effectively.
On an unrelated note, C64 emulation is superb.