Bioshock Infinite, because of the tiresome writing and story that deeply offended my intelligence. At least I didn't pay $60 for it.

Halo Reach. Preordered the Legendary edition and got it home after the midnight release, beat it after about six or seven hours, and sold it the next day. It was a terrible game and not much fun. Yes I know I said I beat it, and why would I take the time to do that if I didn't like it? Simple, I don't like leaving games unfinished unless they are downright unplayable. I just regret paying over a hundred bucks for that waste of time.

Sine Mora.

Diablo III... I bought while working in Korea, and unfortunately, even though most versions have a language option, the Korean version doesn't.

Blizzard categorically refused to help, first knowingly giving bad advice (such as try to take it back to the store) and then telling me that since they "answered my question", they would simply close any further tickets on the issue.

Seriously no Don't Starve? I even forgot the game's title because I never ever involved with it anymore.

Just personal preference, I really don't like a pointless game. Your main objective is survive. Nothing else. Sure you could do some interesting things while surviving but really, thats the main and only thing that matters. I'd like to call that pointless.

Well I bought CS:GO by mistake when it was on sale (17 Mai 2013 5,49€ Counter-Strike: Global Offensive). The funny story is that I got more money by playing it on steam cards "fieber" and cs:go items "fieber" (when crates were still 1.5$) and selling the items, than I payed for the game. Other than that, I like all the games I own (rpg / rts / tbs mostly).

I try really hard not to end up with these, but if you buy enough games its inevitable:

Nuclear Dawn - if you want a hybrid rts/fps, just buy Natural Selection 2

Bioshock - maybe I would've liked this series if I had bought and played it when it first came out. Now though? Bleh.

Sonic Generations - I got a key for a steal, but even so all this made me was miss 2D Sonic even more.

Command & Conquer: Red Alert 3 - Fuck EA for ruining C&C.

I have around 500 games and I like all of them.

Borderlands 2... Twice.

First time: I had planned on waiting for a price drop, or a GotY or something. The game looked flashy, but it seemed as if they dumbed down the loot mechanics from the first game's very Diablo II like system, which was a big part of why I loved the first so much. However, a friend convinced me to buy it for full price so we could play on XBL. Not only was I just as disappointed as I thought I'd be (Good game? Sure. Great game? Maybe. As good as the first one? Hell no), but his wife ended up leaving him and taking his 360. We got to like level 17 together. Lol.

Second time: I am a console gamer through and through. Many games on PC I ultimately play with a 360 controller. That said, I'm a poor bastard and can't afford console games, so I often resort to PC games, which are more easily acquired for free (not necessarily piracy, but giveaways, trading, etc). Having played BL2 on the 360, I wanted to try the DLC, mainly to use new legendaries and raise my level cap, so I decided to get it on the PC, where I could easily buy both the game and the DLC with TF2 keys. I bought the game first, but ultimately I still haven't gotten the Season Pass because no one wants to sell it for less than 11 keys. So now I have a PC version of a game I already have (and prefer to play) on console.

gmod... and quite a few bundles game

Atom Zombie Smasher, Aztaka, Bunch of Heroes, Dead Horde, Depths of Peril, Fairy Bloom Freesia, Go Home Dinosaurs, McPixel, Organ Trail, Plain Sight, Postal, Postal 2, Serious Sam Double D, Sol Survivor, Star Wolves 3, Super Sanctum TD, Turba, Wanderlust: Rebirth, Zafehouse: Diaries.

Fallout New Vegas. Mass Effect 1 and 2. (Played 1, ditched it, haven't played 2 yet, wouldn't want to without finishing 1 which I don't expect to do ever).

Chivarly, paid $6 when i couldn't run it on my laptop. Now that i can run it on my desktop, it's still mehh.

Guardians of Middle-Earth.

Borderlands 2: It was a huge disappointment for me, some people say that it's the best game ever but for me it's just another disappointment. First of all: It's un-optimized for me as hell, getting blue screens of deaths from it randomly while I am supposed to meet the system requirements. Second of all: Am I the only one who pissing HATES Claptrap? He is the most annoying god damn video-character EVER! And since I get constant crashes, that should sum it up.

Under The Ocean: I never in my life saw such a messed up, senseless game ever. It looked fun as hell, then I started to play it and it just had no point, I can't craft, I can't do pretty much anything because all you do is run around allover the place on some island, collect some food and keep your character well-fed, sometimes even make a fire but other than that it's just plain boring and crafting didn't function to me even after collecting a thousand stuff. You can tell me the usual "You are stupid, you just didn't know how to" line, but to be honest: I don't care. If I can't figure it out by myself after 6 hours of gameplay, then f*ck that game.

Walking Dead: 400 days: Contains about 6-10 minutes of gameplay, being a complete senseless mess that rushes the introduction of each character. It sucked so bad in my opinion, that it made me lose my apetite for The Walking Dead as a whole. I might just won't play Season 2 because of it. Some of the characters are outright annoying and stupid anyway.

W40k: Space Marine: I love this game from the deepest parts of my heart, but I have to admit that I regret getting it greatly. Why? Because it's such an un-optimized piece of sh*t that it's annoying already. Every multiplayer game gets interrupted all the time by "Merging to a new host" occasional laggy people who suddenly teleport in front of you and you are dead, random slow-mo bugs and FPS issues. So as much as I want to love this game I simply can't and I just add it to the disappointment list.

I could go on forever to be honest, but these are the most mention worthy ones.

Red Faction Guerrilla.

Ace of Spades.

Bloody Good Time. I have no idea what possessed me to buy it.. Other than the fact that it was a steam sale.

It is kind of fun to a degree I guess.. but.. yea.. Not to mention the false positive that the game has with almost every anti-virus and maleware program in existence lol.

Amnesia: The Dark Descent. Played it in offline mode one of the times my internet went down. Not as scary as people claimed, and the game itself is for the most part fairly boring to me.

I have a few other games that could possibly end up on the list if I ever get around to playing them though..

edit
Frozen Synapse gets added to the list. ( Someones post made me remember it lol. ) Though I did not exactly pay for it as I got it during the steam coal/gift thing. I got it in trade for something if I remember correctly. Played it and did not like it as much as I thought I would after I had watched someone else play it. :( One day I might give it another try though and that might change my opinion.. till then...

Omerta City of Gangsters; Virtually no interaction on the main screen and possibly the least fun turn based combat I've ever played.

These are only the games I've bought via steam and are dissapointed at. I have probably 10-20 more, but they're from bundles and I didn't technically buy it for those games.

Max Payne
I'm sure it's a good game, but it's too outdated for me now. Clunky controls and terrible checkpoints/saves.
SEGA Genesis & Megadrive Classics
Same here with bad controls and a genereally slow emulator.
Delve Deeper
Simply a game I didn't like. I didn't understand it
Terraria
I just don't see the point of it at all.

Unreal Tournament 3.
I love the Unreal series, and when I learned about that UT3 is coming out I was so excited, and when I saw the trailers, I've totally got a headplosion. However when I bought and tried it, I've been really upset. It wasn't like the older ones, nothing about the Tournament. The game itself would be still good under the name of Unreal, but since it's not about the championship, they shouldn't have called it Unreal Tournament 3, but rather just Unreal 3.

Saints Row IV

Pretty fucking average; the second half of the game is just painful. Should have been a standalone DLC, like Blood Dragon.