So many times. So many times.
Where do I start?
Castlevania: Lords of Shadow
It starts out rather strong, but as more and more mechanics are introduced, you find yourself watching too many meters at once (Health, Ammo, Light, Shadow, Focus. All in different fucking corners of the screen!) which makes keeping your focus to pull off the more intricate combos harder. On top of this, you have to watch for enemy tells, too. Like the block breaking attacks.
Dante's Inferno
The Lust Tower boss fight in the early game is really the peak. You're on an elevator, chasing a giant Egyptian queen as she climbing, fighting off hordes of enemies and it's just epic, really.
Half Life 2: Episode 1
And it's just Episode 1 that I had the problem with, really. I had a lot of fun during the early parts before you found a gun, when you just had the Flashlight and Alyx had the gun. After that, it bored me for the next 2 hours. Short game is short. On the plus side, "The One Free Bullet" was fantastically fun to get!
Red Dead Redemption
It starts out pretty strong, but once you get to Mexico. UGH. Mexico just sucks after you finish the Landon Ricketts missions. All the Mexican Army and Rebel shit just killed the pace, and the game, too. (I stopped playing there TWICE, only beating the game on my third attempt) And everything after Mexico never recaptures the same feeling as the first third of the game.
Mass Effect 2
Good intro, then I realized the gameplay lacked any more depth past it. I was hyped for the game, too. Even replayed Mass Effect 1 to 100% completion (including mineral hunting and all the stupid collectibles) the week before release for a shiny new save (Vanguard, Paragon, Male, Kaiden) to carry over. Great game, piss-poor RPG.