Banshee, a vertically-scrolling shoot ’em up released by Core Design in 1994, is a great example of beautiful 2D graphics on the early 16-bit machines.
Although – as a shooter – Banshee is only just about okay (not bad at all simultaneous two-player), but the graphics are wonderfully stylised and extremely well coloured and drawn, and really make it something special.
More: Banshee on Wikipedia