Mine would have to be Jim Power The Lost Dimension in 3D.
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This is the SNES port of a 2D action platformer on the Amiga. It's not very good for many reasons. One of the worst parts is the visuals. They messed up the parallax scrolling in the SNES version. The background just doesn't move the right way. Some people can't even look at the first stage without getting ill. It arguably gets worse during the shooting stages where the screen never stops scrolling. It's really distracting even if it doesn't provoke a visceral response.
The difficulty is also pretty brutal and requires a lot of trial and error memorization. You die in one hit and have limited continues to beat the game with. I've beaten it on emulator with save states between levels, but even then it was really hard.
The game isn't all bad. The soundtrack was composed by Chris Hueslbeck of Turrican fame and was really good. The music for the first stage gets some flak because it sounds really similar to the lava cave theme in Y's 3. I like the Amiga versions better, but the SNES has a few exclusive tracks that sound decent. Some of the SNES exclusive stages are also kind of alright if a bit heavily deriving from the top-down stages in Contra 3.
If I had to explain why I like it, I guess it would be a combination of the soundtrack and the really horrible scrolling. It's weirdly charming in spite of the rather tedious difficulty. Here's a longplay if you're curious.