Haven't read the whole thread, excuse me if these have been mentioned already, here are just a few artistic or great Amiga games to check out:
Apidya - This silky smooth side-scroller is the best SHMUP on the Amiga, fullfukkinstop.
Battle Squadron - Raw and gritty vertical-scrolling SHMUP, runs at full frames.
Agony - Thumping soundtrack and gorgeous visuals, the game is art. Game-play sux ass, though.
Xenon 2 - Only for the sampled soundtrack, three layer parallax and stunning pixel art, game-play isn't quite there due to running at half frames (a trade-off because of sheer amount of shit going on).
Gods - Very deep 8-way scrolling ancient greek-themed platformer unfortunately somewhat letdown by clunky combat and Atari ST restrictions (colours, scrolling and framerate of many Amiga games were nerfed due to coding them with inferior ST in mind, and just doing lazy-ass ports).
Lionheart - hack n slash platformer, perhaps the prettiest Amiga game ever made. Bizarrely bad animations and short attack swing, though. Still, more fun than Beast series.
Turrican 2 - 8-way parallax hardware scrolling, and probably the most highly revered Amiga music (Chris Hülsbeck). the 360 degree rotating gun is boss.
Flashback - often confused with Another World, FB doesn't quite match the artistry but more than makes up for that with excellent game-play.
Syndicate - isometric tactics with cyborgs, the freedom of play extended to attacking innocents.
Speedball 2 - top-down "pinball-stye" futuristic brutal sports football. The remakes suck, play it on original hardware, UAE or not at all.