WipEout Fusion. Took everything I loved about PS1 WipEout and made it rubbish. Thankfully, they got back on the right track again with Pure.
Command & Conquer 3: Tiberium Wars. Dull & slow beyond belief after the brilliance that was Tiberian Sun, I struggled my way through this game to see the end of the campaign.
SSX On Tour. Never understood why they took the brilliant simplicity of SSX3 and shoved it down a Napoleon Dynamite-inspired cannon. Skis weren't fun either. Pretty big blunder for my beloved series.
Army of Two. My flatmate & I bought it for co-op fun and I was determined that we got our money's worth.
Metroid Prime 2. My best friend raved and raved about how MP was the best series ever. I bought a Gamecube in ~2008 for £30 with a copy of Metroid Prime 2. Played through to see what the fuss was all about. Didn't much enjoy it.
Final Fantasy X. I just wasn't having a good time by the end of the game, but I was determined to see it through to the end. Back then Final Fantasy were the only JRPG's I had played, so it was a pretty scary thought to have to move onto something else. So I kept hoping it would improve.
That's all I can think of for now.