The Atari Jaguar was pretty lousy. I got one off of Ebay years ago, tried it once, and never really bothered with again. Still have it, though, and I don't think I'll ever get rid of it. After all, who could I pawn it off on?
The 3DO had potential, for the era it came out in, but I think it was both too early and too expensive to really go anywhere. According to Wikipedia, it was $699.95 when it came out, and this matches up with what I remember it being way back in the day. Even back then, I felt that was far too much money for an unproven gaming rig. If an eleven year old kid can figure that out, then their parents definitely can.
I can also imagine that most developers at the time were not equipped or prepared to take advantage of its high end abilitis, and investing time in money in doing so (especially when the Genesis and SNES were a bigger and easier market) would have been foolish and risky financial suicide for most. If the 3DO company had planned ahead and gotten some non-shovelware titles lined up, reduced the hardware price, and focused on making the best game system the could - well, it might have still failed, just not so spectacularly. I picked up a second model 3DO and two controllers at a thrift store for $15 a couple years back. Total serendipity. I will say that the Samurai Shodown port for it is pretty decent.
The Sega CD was a good idea that was implemented poorly. The 32X never should have been released. Probably caused the start of Sega's decline as a hardware maker.
Those are about it, off the top of my head.
