Just noticed this thread, good idea op
Anyways, I've got a bunch I thought didn't live up to the hype:
Guitar Hero 3 (songs just didn't feel fun for some reason)
Eye Toy: Kinetic (I was so eager to play this game but it doesn't even start up for some reason)
Ratchet and Clank (just the first one on ps2, replay it now and you'll understand where I'm getting at)
Prince of Persia: Warrior Within (doesn't feel like a sequel to SoT...much more combat than platforming/puzzle, liked the dark tone though)
Zelda: Twilight Princess (just didn't feel fun for some reason, only got so far due to boredom)
Super Mario Sunshine (an entire Mario game based on levels in water...and a dumb shooting element imo, good platforming parts though)
Loco Roco (reviewers were right, it is really repetitive)
Crush (probably because I was expecting a platformer and got a puzzle game)
Jeanne D' Arc (got it since I heard so much praise and hated it, guess I don't like Rpgs)
Ghost Recon (1st one for xbox...worst game I've ever played, by far and I actually heard it was good)
Knights of the Old Republic (Read gamespot's review..."don't need to be a fan of star wars or rpgs to enjoy this game" and well I wasn't familiar with either category, again hated the critically acclaimed game)
Smackdown Vs. Raw 2007 (bad idea changing the controls, Yukes - more too but I can't recall of the top of my head)
F Zero (snes - awful looking game that I couldn't even play for 30 seconds)
F Zero gx (difficulty makes it insanely hard, in a frustrating way)
Grand Theft Auto: Liberty City Stories (half-assed story, half-assed controls, half-assed music, half-assed everything in that game!)
Xbox Music Mixer (it's not even compatible with most songs/cds)
Bomberman (psp - just not fun)
Unreal Championship 2: Liandri Conflict (I heard it was a combination of Halo and Super Smash Bros...dodging rockets and whatnot, still a good game but not as good as I heard it was)
Perfect Dark (more of a 007 guy, never liked PD)
Clubhouse Games (some of the games aren't fun at all and w/o multi it gets boring fast)
Golden Sun (tried it since I heard it was like pokemon, only rpg I can stand for some odd reason, but hated it..)
Mega Man: Powered Up (1st Mega Man and the difficulty was too much with the bosses, found out it should be played on easy first though...lessens the fun/intensity)
Wipeout Pure (just not feeling the fun in it, good race tracks though)
and lastly
Super Smash Bros. Brawl (fwiw, my early vote for goty 2008, but I was expecting a bigger update then what we got with items and whatnot...it's been 7 years since the last one!)
Oh and Metal Gear Ac!d 2...what a letdown