The SNES gives you a lot in hardware including stuff like amazing transparency effects, scaling and rotation of a single background at 60 fps, gradient fills, shape drawing (like triangles or circles), lot's of color, 3 layers of parallax scrolling, 8 channel ad-pcm audio, etc..
The Genesis doesn't give you even close to that in hardware (it's 2 years older after all), but the graphics hardware is very simple and easy to program. It also uses a chunky graphics format, but on the positive side, it has much more VDP bandwidth and arguably the best CPU of the time.