Too many to count, but some notables include-
Medieval 2: Total War. Despite how much I love RTW, M2 just sucks balls in comparison (which is odd since it is the sequel to Rome). Empire was in the same boat, until I played it enough to get into it.
CoD Mw/WaW/MW2. All fall into the same category. Campaign is bland and worthy of 1 or 2 playthroughs and multiplayer isn't overly fun. I don't do online gaming, so I get really annoyed when split-screen is ousted or degraded. Perfect example is the Heartbeat sensor in MW2, tis worthless in split-screen since you can't see but the top 3rd of the thing at most.
Killzone 2. I liked KZ1 and played for hours in single-player against bots. For some reason, couldn't get into KZ2. It would help if I could see anything besides the glowy eyes (damn Next-Gen graphics).
GTA4. TOTAL crap. GTASA is SO much better. Cars handle like poo, weapon choice is too limited, and it steals too many ideas. The phone is taken from Saints Row (but at least SR would pause everything when you tried to put in cheats, targeting from Scarface, and the police-evasion system is a 100% DIRECT rip from Scarface (Scarface being a much better game). Usual vehicle selection include a taxi, another taxi, a third taxi, and to spice things up a bit a taxi van. Not even falling from a helicopter was fun. You just bounced a tad and that was the end of it. It in no way deserved a 10, more like a 3 at best.