Honestly the console not to live up to expectations the most would have to be
Wii. I remember telling everyone how Wii would change gaming and it would be the real experience right before it came out. Then I bought one and realized that aside from first party's the Wii was severly lacking. After trying to some other games and seeing how Wii-mote controls were just shitty and tacked on I decided to return it. I wanted fun good third party titles and for the love of god 1 to 1 tracking but so far it's just been useless wiggling with gamecube graphics. I've been a nintendo fan my whole life since NES but(and I know Wii fanboys will hate this) controls are perfectly fine on a controller and most Wii-mote controls are cumbersome.
You know what I guess too the fact that the ps3 doesn't have many jrpgs really disappoints me. I Love rpgs and I assumed the ps3 would have them, the only saving grace is i got a BC ps3 so I get to play all the RPGs I want really.
For the 360 I would just say the hardware and userbase plus paying for online. I will not pay for online I as a PC gamer too think it is just unacceptable. Plus most xbox fanboys I know treat it like it's the ps2 of this generation.
And you know what..Fuck PC developers that program for only the zenith of gaming computers, COD4 is a prime example of the opposite of that, I saw that game run very well on a 6600 geforce with a gig of ram at good fps.
Can love bloom on the battlefield? Proud supporter of this gen!!!