>>11947720
They are pretty good; the earlier ones are probably better, but Land of Illusion (the second Mickey game) for example is excellent even if it's less challenging than Castle of Illusion (the first one).

Also be advised that Castle of Illusion isn't a port or downgrade of the Genesis game; it's its own thing except for some similar level themes and enemies and a must-have for anybody who owns the system.

>>11947769
No, the GG can't display more colors than the SMS but it's got a much larger internal color table to pick from (even bigger than the Genesis' for some reason) and sometimes devs took the extra time to make use of that. In the case of the Disney games released for both systems though they are visually identical; the only difference is the screen real state so the SMS versions are much preferable.