FEAR 1
FEAR 2 (I should have got my lesson with the first one)
Lost Planet
Condemned (think I'm done with Monolith Productions)
Red Steel
Sonic and the secrets rings (controls...ouf!!)
Batman Arkham (a good game just not my type)
Gyrostarr (on wiiware)
Prince of Persia (2008) so bad...
Battlefield: Bad Company (worst game ever IMHO) I can avoid a fight in campaign just by entering a base by it's side...tow enemies npc in front of each other (about 1 feet) and not attacking each other...wow.

thats about it.

There's only been a couple of titles that I've actually regretted buying/playing this generation:

MadWorld (Played the first level... that was all I needed to know that this would not be my kind of game.)

The Conduit (*Shrugs* Got it as a gift, so I didn't feel that bad trading it back in a couple of days later.)

Yoshi's Island DS (It's like Yoshi's Island, just without the charm. Oh, and there's even more crying babies. Blech.)

I will remind everyone that these are my opinions.

Final Fantasy XII: I am huge Final Fantasy supporter, but I just couldn't adapt to the new battle system. (The Only PS2 game I've ever regretted getting)

The 7th gen got me good however

Guitar Hero 3: Hype is what got me here. I quickly found out that this was not my type of game.

Blue Dragon: I was hungry for a 7th gen RPG. I was quickly turned off by the story, characters and voice acting.

Halo ODST: I'm actually playing this right now just so I don't feel like I burned the 60 dollars I paid for it back in October. The story is extremely boring. The new visor system that is supposedly help you be stealthier is basically a flash light that adds no real stealth elements to combat, and I now have two copies of Halo3 online...

Assassin's Creed: Bloodlines: I knew it was going to be a load of shit that would feed off the success of AC II, but I still got it because I'm a fan of the story.

Oblivion: I cannot understand the praise and love this game gets. It is the most shallow experience I've ever had in gaming. The story was so vague, and the environments, although extremely vast and beautiful and full of useless pickup items, were empty. I felt so deserted and isolated playing this game that I had to leave my home to remind myself that there IS life outside.
... I was also very annoyed by the "item capacity/weight" system. I was simply overwhelmed by the amounts of objects you can pick up because I always felt like I was leaving something important behind.

Fallout 3: *See Oblivion* I started to pay very close attention to developers after I made this godforsaken mistake. I forget who wrote it, but the VGC review of Fallout says, "Oblivion with guns."

Uncharted: Drakes Fortune: The 3rd person shooting system did not sit easy with me. Camera angle (especially when they automatically went to an annoying angle) made me dizzy. The puzzles were not fun at all. I personally felt the game was rushed.

Killzone 2: This game was pure awesome, I just sucked at it. The controls held me back from enjoying it though. I don't think I was ever able to win an online match. In fact, I strongly believe I was the reason my team lost everytime I joined a game.

~honorable mentions~

Folklore
Afrika
Dead Raising
MGS: Portable Ops

I thought it was going to be FFXIII, but well... No...

In recent times, Bioshock 2 - jus wasn't as original as the first. then pinball hall of fame on ps3 then 360 both sucked. finally assassins creed 2, not as good as some say it is, though i only played it for like 5 mins so... might change my mind later.

Not really certain games. But I really SUCK at fighting games except the WWE SvRs and FF Dissidia. All the other ones I have bought suvh as SC4 and SSBM I wish that I hadn't.

How could you not like SotC :0
I didnt like
FF1 PSP REMAKE(I got stuck on a part and the enemies were TOO EASY)
FF2 PSP REMAKE (Dumbass attack system or whatever)
FF7 DIRGE OF CERBERUS(Forced myself to beat it)
Oh and Super street fighter turbo HD remix(I liked it just that i couldve gotten something else)

@seraphic

I don't think it's fair to judge a game based on 5 minutes of game play. I'll start losing respect for ya :P ... some of those games on my list I've played for over 20 hours before I came to my conclusion.

Modern Warfare 2

As if your pathetic Nintendo bashing agenda wasn't clear enough...

On topic there are literally hundreds of games I regret buying so I'll stick to this gen and still likely miss tons.

Wii:

Red Steel, Far Cry, Medal of Honor Vanguard, Monkey Ball, No More Heroes both 1 and 2, The Simpsons Game.

360:

Condemned 2, Assassins Creed 1, Perfect Dark Zero,

PC: 

The Saboteur, Gears of War 1, Mirrors Edge.

eeps I do not think I can play a game for 20  hours I did not like. Useually I see if my little cousin wants to try them after 1-2hours,if not sell them. Thankfully I do not have to sell them much.