WizKid was a lot of fun ... I think I've completed it, but I'm not sure.

As for the first Amiga game I've ever completed - hmm, that's a tough one. It might've been The Great Giana Sisters. Incidentally, it was also the first game I got after I purchased my Amiga, so there wasn't much else to play at the time!

I used to have a much better "completed games:unfinished games" ratio back in the day, even though I had a lot more games for the Amiga than I do now for the PSX/PS2/PC/GBA/DS, that's for sure.