Yeah, I thought the bitmap brothers did a great job with anti-aliasing and making 32 colors look impressive. Not sure if they used any more than 32 on the OCS/ECS stuff. Most of their stuff is subdued and on the dark end of things, so they could use color 0 (black) to their advantage to get some extra detail. Gods/Speedball II are good examples of this.
Sachs, on the other hand just painted real world objects mostly, but I think as stills, and without HAM mode, they're some of the best examples of early 16 bit art.
Can't mention game graphics without mentioning psygnosis' SOTB series, I still think they're all excellent, regardless of gameplay....