Another year that an excellent Mega Man game loses to Mario. Super Mario World remains my favorite Mario game of all time. The game felt like SMB3 on steroids and brought a whole new cast of enemies as well as Yoshi. The cape was an incredible power-up (almost too incredible) and the ability to throw items/enemies up added great ideas in gameplay - a feature that has finally returned in the upcoming Super Mario Bros Wonder.
The colorful graphics, excellent sound effects and wonderful world along with its humor and whimsy make it my game of 1990 by a wide margin. It's simply one of the most enjoyable games you can play.