The Atari 5200. This console could have been something very special but the bad controllers, the lack of support from Atari and the some other odd design quirks doomed it. I thought the graphics and sound were good and some games were better on the 5200 than the CV but all its flaws killed it.

That's my pick. The 5200 was expected to be a contender. A console like the 3D0, the Atari Jaguar or the Virtual Boy was destined to fail even before it hit the market.