I too am always on the lookout for quality platform games - especially 2D.
Since I bought a peecee in 1995 I have played a couple of good 2D games designed for this machine:
Duke Nukem Manhattan Project
(2001): it is pseudo-3D and one of the few games I actually finished without cheating. Last weekend I saw this game for only 2 Euros at a toy shop.
(not sure about the title) (1997): starring a muscled blue duck in a multiscrolling platform affair. Very reminiscent of Earthworm Jim
Jazz jackrabbit 2
(1998) is the best of the lot. Very much Sonic