Killzone 2. I simply HATED the heaviness of the game. Completely ruined the experience for me.

Are you sure? check again.

DISAGREED!!! LOL there should be a DISAGREE BUTTON like N4G LOL

Final Fantasy 13 - i didn't really hate it, i just though wow the bosses have such long life bar LOL, the main reason i didn't complete it was because around chapter 7, i was fighting a boss, Killed it, Loading..... Loading...... Loading......, Turnt off PS3, Did it again, Killed it, Loading.... Loading....Loading....... Ebay (SELL) 30 POUND BUY NOW LOL!

Devil May Cry 4 - That game was SOOO BORING

Me too.

Killzone 2

Is really the only game that iv purchased.

I rented several though

Eternity's Child. I thought it would be a cool indie game, but it was just terrible. just a look at the "achievements" page tells all: http://steamcommunity.com/stats/EternitysChild/achievements

cod mw2

For me it's mainly the fact of losing interest of playing the game, not that it is really bad.
Though many old school games come to mind, but from this generation I'd say Ironman.

Buck Bumble N64

Jedi Knight 3 Xbox Game breaking bug caused a mission with Kyle to bug and I had no other save file:(

I was lucky enough to rent Two World's and not finish it.

Blacksite: Generic military alien game that stuffed up a lot and didn't have rumble.

The Orange Box: I was told it was better than Bioshock, but the gameplay was extremely bland, the atmosphere just wasn't there and it just failed to meet my expectations. I feel I have an obligation to play it though, so I'll give it another try one day.

Jericho: Wasn't a bad game, just wasn't interesting enough to keep playing.

Red Steel: My first Wii game, it was just horrible, it just did everything wrong.

Gears of War 2: Just to similar to the first one (which was just fantastic), after I got underground into the caverns I just got bored.

Oh hell yes! I bought too many games that I just couldn't finish, although it wasn't necessarily because they were "bad", it was just that they couldn't keep me entertained long enough.

Some of these games are Too Human, The Simpson's Game, Lost Odyssey, Mass Effect, Lair, Grand Theft Auto 4, inFAMOUS, Folklore (Mainly due to looking to far into strat. guide), Resistance 2 and Gears of War 2.

I am sure there are more but those are the ones that come to mind. I would have added Uncharted 2 as well but I know that me ditching that game was only due to the release of FFXIII.