One I really enjoyed was Space Quest, I was surprise to see Space Quest 5 in Amiga Future mag recently as one of the title you can now play with ScummVM, will be definitely checking that out.
Star Trek 25th Anniversary a great AGA game that requires quite a bit of Amiga grunt, its shame the voice version never came to the Amiga.
If you have a high power Amiga, one game I always wanted to try was Nightlong, port by Clickboom, An off topic question but does Nightlong work on OS4?
I know you after more obscure games, but just encase you not played them, I would recommend them.