The Misadventures of Flink (Sega CD)- A Psygnosis game on a system that didn't make much of an impact in the gaming world. It has a lot of visual detail, some nice music, plenty of platforming, some spell making, and a good challenge level. The controls are good, and it has a solid graphical style. Given the system it came out for, it's easy to understand how this game got overlooked.
Tinhead (Genesis)- Spectrum Holobyte made this game. It came out of nowhere, but proved to be quite the entertaining platformer. Good graphics, good tunes, four worlds with three big levels each, an interesting weapon setup, and it offers a decent challenge. It didn't get much attention back in the day, but it's worth checking out.
Ristar (Genesis)- This game is fantastic. Beautiful graphics, great music, large levels, a solid challenge, lots of speed, an interesting gameplay twist (stretchy arms)... it does so much right, yet didn't get half the attention it deserved. It's a bit more known thanks to its being included in some Genesis compilations, but it's still an underdog.
Blades of Vengeance (Genesis)- An EA game? Nice graphics, good tunes, large levels, a solid challenge, and three characters to choose from. The only downside, is that the game is rather long, and there are no saves or passwords. Sure, it's part platformer, part hack 'n slash, but it's definitely a little seen game that's worth a go.
Alisia Dragoon (Genesis)- The only cartridge game Game Arts made for the Genesis, and it's a great one. Very good graphics, enjoyable music, an interesting weapon system, and a good challenge. It came and went with basically not hype or advertising, and that's a shame given how good it is.
Awesome Possum (Genesis)- Well, Tengen tried. They took an eco-friendly idea, and tried to run with it. The problem is, they didn't try hard enough. The graphics, while not bad, don't stand up to the other games I've mentioned. The music, while not bad, falls into the same category. The frame rate, as odd as this sounds, has a hard time keeping up with the game. It feels like it's running at about 15 fps, which causes problems when you start moving fast.
The sad part is, they did a few things right. Big levels, the character is actually lip synced to his sayings (and there are a lot of them), and the between levels questions can be fun. But the technical issues overshadow the few things that work. Even so, give it a try. Who knows... you might like it.