Easily my Wii disappointed me the most. I'm not saying I didn't have fun with it (before it ultimately broke and refuses to read discs now... ), I just thought the motion controls would be much better than what I got. I remember wanting it for Star Wars: The Force Unleashed because the thought of swinging a controller as a lightsaber was like the coolest thing for me. While I still enjoyed that game greatly, the controls were less than enjoyable, and swinging was mainly a chore and I would usually end up getting tangled in a nunchuk wire... Oh, did I mention how annoying the nunchuk was? Using that thing made my hand hurt so much, even to the point where I didn't want to play games that required it...
The game selection was also slightly disappointing for me, but there were a few great games I owned that I spent hundreds of hours on, like Wii Sports, Super Mario Galaxy, and Mario Party 8 (though, I was a bit disappointed with 8 and still prefer Mario Party 2 on my Nintendo 64 ).

I would probably say between the Phillips CDI and the Virtual Boy. I got a friend that owns both of them, and they are just very disappointing. There are a few fun games for both, but I couldn't play them for more then 40 minutes each, they are just not well designed systems at all.

The 3DS is easily the most disappointing game system I've played. I don't know exactly what it is, but I just can't make myself enjoy playing on it. In all fairness though, aside from the PS Vita, I've never cared much for handhelds.

Excuse me, Miss Nexoria. I think you might have been missing out on some really great exclusives. Have you ever played Dance Central, Dead or Alive 4, Dead Rising, Fable 2, Forza Motorsport 2, Kameo, Left 4 Dead, Mass Effect, Otomedius, Perfect Dark Zero, Popcap Arcade, or 'Splosion Man? Also try Project Gotham racing 4, Castle Crashers, Battleblock Theater, and Infinite Undiscovery. Just thought I'd let ya know, my friend.