What's the most disappointing game system you've ever owned? Did you keep it? Did you trade it in? What games did you have on it?
I hate to say this but Nintendo 64. I owned one as a kid and loved it. Then I bought one to collect for six years ago. The system just has not held up well over the years. Many games on the system like Goldeneye, and Turok aren't classics. They're just old. I can't get over the N64 fog when playing games like Rogue Squadron. True classics for the system like Zelda, or Starfox were remade for another system ages ago. Collectathon platformers just kind of all feel the same. IMO it was a revolutionary system for it's time, but N64 just has not aged all that well.
I wound up trading it in eventually.
Banjo Kazooie (The best collectathon platformer IMO)
Conker's Bad Fur Day
Super Mario 64
Resident Evil 2
Ocarina of Time (20 FPS has not aged well. Get the 3DS version!)