Back in the day, I played a lot Super Baseball 2020 on the SNES with a buddy. Good port, but nothing special. Not enough to call it gem.
More recently I really fell in love with the Genesis port of Viewpoint. Technically it's a mixed bag, it offers 60fps, but flickers and slows down a lot. Some graphics took a cut and musically it's just ok but... somehow it still manages to capture what made the original so fascinating. How is that possible with all those audio-visual inferiority mentioned? Pretty simple: brilliant gameplay. Turns out that VP wasn't just an awesome graphic demo some deemed it to be, and proving that is the real surplus value of this port.
Last but not least, there's Twinkle Star Sprites on the DC, which offers the more complete experience than the original due to its slowdown on/off option. Excuse me, that's sprite limitation of course hehe...
Honorary mention goes to the Sengoku Mega-CD port. It comes with an asid approval, too.
BTW it's a shame Andro Dunos never made it to the Super CD. I bet that port would've managed to run w/o the infamous elevator flickering in the second stage. Because, well, 8bit, I guess... so it would have run on native hardware, right?