The Most Disappointing Game Ever?

I will always maintain that Dragon Age II isn't the spawn of satan, but even as an apologist for that game, disappointing is the only way to describe it. And of course, KotOR 2 was the original unconventional sequel that was worse for being unconventional, although we can probably blame the change of developer on that.
 
However, while Dragon Age II is competent and KotOR 2 is a bad memory and a CD case on my shelf, I couldn't imagine how totally and utterly soul crushing Master of Orion 3 was for people who liked the second game. While the phrase "takes everything good about the older games and throws it out the window" is perhaps a little cliche, MOO 3 is the ultimate personification of that. It's a 4X space strategy game with no personality, the ugliest and least intuitive UI I may have ever seen, and to top it all of, it practically plays itself.

Hellgate London.

Killzone 3.  i put that game on such a high pedestal.  i thought they could only improve the story and make it much more epic...  but i had no idea that the people that wrote the story were actually baboons.  this year has been disappointing because i thought this would be Sony's year.  so far the exclusives havent been up to par with my unusually high standards.

Forza 2, Killzone 2's multiplayer and Rise of Nations.

Two Worlds. I really wanted this game to be an Elder Scrolls IV clone. The screen shots looked cool, and b4 it came out a bunch of editors were calling it an Oblivion clone. Then when it came out, it wasn't :-(

Dragon Age 2 was a real disappointment. Not the worst game I've played by a long shot, but I loved the first and they killed everything I loved.

Flower was hyped and crap.

Dark Sector. What happened to my space ninja saboteur, instead all I got was generic dude with a weapon straight out of the movie Krull and essentially everything else that screams generic.

Banjo-Kazooie: Nuts and Bolts. I still loved that game, but I really wanted the third Banjo game to be like the first two. I miss the platformer days.

I might get some flack, but Persona 4. Sure, it fixed all the gameplay problems of P3, but the story and characters just didn't measure up. And the ending... talk about Deus Ex Machina.
 
Fire Emblem: Radiant Dawn also sucked major balls. Path of Radiance is one of my favorite games of all time, and this just spat on all its accomplishments.
 
I also didn't get the hype pay off from...
Modern Warfare
Enslaved (Brad's hype)
Wind Waker (if they just got rid of the sailing...)
Baiten Kaitos (played the sequel first; it was way better)
Twilight Princess
Tales of Symphonia( two of my best friends attest this to be the best game ever, couldn't get past the beginning)
Indigo Prophecy
MGS Peace Walker (unplayable)
Zone of the Enders (Kojima)
Kingdom Hearts II  
PoP: Warrior Within (interesting story, awful everything else. Glitchy as hell)
Jak II
Half Life 2
GTAIV
Darksiders (everyone on Giantbomb's guest thing put it in their top 10 last year)
Assassin's Creed: Brotherhood (great, but not as great as the bombsquad said)
 
 
My life is apparently full of disappointment.

Star Wars: The Old Republic. I know it's not even out yet, but what I expected was KOTOR III. I don't know if anything has disappointed me as much as this before.

Maybe also Splinter Cell: Conviction

1. Bioshock 2
2. Scribblenauts
3. Brutal Legend
4. Far Cry 2
5. Resident Evil 5
   

Can't name a worst game "ever" as there are potential shitty games coming out in the future.

Far Cry 2 just kinda slowly petered out for me, and I never even got to the second half of the map. I mean, it was okay, but I just lost interest. Also: They gave you fucking Malaria, so there's that.

Spore was kind of a bummer too. I mean, it's a fun game but...it just could've been more. Especially the Space part.

Modern Warfare 2.
 
Honestly Call of Duty 4 was a brilliant game with a decent balance of online and single player. Story was tense and had some standout moments and the online was clean and fast. MW2 however destroyed an interesting story and spammed a multitude of killstreaks and perks which turned the online into a mess.
 
Also Resident Evil 5, co-op is fun but Resident Evil 4 was so good. Just seems like a step back.  
 
MGS4. Love the series. Love all the games. But they made it more of a shooter rather than concentrating on the stealth, only about two acts can you use stealth but it didn't feel as thrilling as the previous titles. It also was a short experience in terms of actual gameplay. MGS3 is amazing and I wished they just improved on that formula rather than create a shooter. It was reaching out to a wider audience to justify the budget spent on the game but ultimately I think it created a disappointing conclusion.