That Game You Feel Has Potential, But Completely Failed Delivering.

[Raggedstar]

Jak 3
Still good, but didn't have the heart of the first two. When I'm playing a platformer, I don't want to think "Can I platform yet?" *waits another few hours* "Ok, I know you're proud of your wonky vehicle physics, but can I platform NOW?". Until you're sent to the temple (about 25% in), your platforming after the tutorial is ZERO. When you return to Haven you get to do some solid platforming. But it's just so unbalanced on when you encounter those platforming sections. Oh, and the plot was a clusterfuck. Who's idea was it to make Jak and Ashelin (who he has no chemistry with) together with no lead-up or reason? AND toss Keira in the bin?

(while I'm on that note)
Jak and Daxter: The Lost Frontier
Want a surefire way to mess up a platformer? Making 30% of it lengthly dogfighting sections. If those were reduced, fixed the camera, fixed the script a touch (and actors, though at least Daxter is back, being the least expedable), and maybe bring in more connections from the trilogy, and you could've had a decent game. Not Naughty Dog good, but better than what they released.

Mirror's Edge
Already been mentioned.

Spore
Again, already mentioned

Sonic Unleashed
Toss the werehog, the mission hub crap, tweek the level design, and make Sonic slower and Unleashed could've been pretty damn good. The pieces were in place for something good, or at least better. (Edit: The main theme was called "Endless Possibility"...I see what you did without me knowing, brain)

Edit:
Skyward Sword
Can't believe I forgot that! Nintendo wanted create a standout and something original from the series. They almost had it. A bit slow to begin, but they could've had something more character driven and a different kind of story. They had it...but then they pissed it away by making things extremely padded and filling it in with pointless "proving your worth" and sidequests that waste your time. Fi was an interesting idea, but they made her never shut up and be captain obvious. There is a bunch of other stuff, but I don't think I need to mention it. Good game with a lot of bad decisions. That's how I'm describing SS these days.

 

[217not237]

Mindjack. The whole "control other people" thing sounded original, it looked like an enjoyable game, but, to quote Ben "Yahtzee" Croshaw, "Mindjack is fucking, fucking, fucking, fucking bad, bad, bad, bad. Don't, don't, don't, don't play it!"

 

[putowtin]

star wars the force unleashed both 1 and 2. it really had some good stuff going for it. but both were to short and the charater was way to overpowered and the story was shit.

This, the fact that a game studio could finally explored the previously black hole that was the time between Papa Palpatine taking over and "I'm on a diplomatic mission to Alderann" and they messed it up was fustrating, and making what could have been the most exciting Star Wars games since KotOR I & II into a button mashing mess was disgraceful, but leaving a series on a cliffhanger that we'll never get a conclusion to... ahhhhh!

 

[scorptatious]

Jak 3
Still good, but didn't have the heart of the first two. When I'm playing a platformer, I don't want to think "Can I platform yet?" *waits another few hours* "Ok, I know you're proud of your wonky vehicle physics, but can I platform NOW?". Until you're sent to the temple (about 25% in), your platforming after the tutorial is ZERO. When you return to Haven you get to do some solid platforming. But it's just so unbalanced on when you encounter those platforming sections. Oh, and the plot was a clusterfuck. Who's idea was it to make Jak and Ashelin (who he has no chemistry with) together with no lead-up or reason? AND toss Keira in the bin?

I have to agree with the last bit. Jak and Keira have been trying to get together since the first game and then she gets tossed to the wayside during 3. That's the one thing I disliked about Jak 3. Other than that though, I thought it was a good game.

OT: Sonic 06 for me. I LOVED the Sonic Adventure games. Especially SA2 Battle which I think is a classic. So I came into Sonic 06 expecting something far greater than that. Instead, I got an unfinished game that was glitchy, slow, had atrocious loading screens, a bad story, bad new characters, and overall a bad experience.

I couldn't find myself playing this game after beating Sonic's story. So I watched the rest of the game on Youtube and holy shit was it bad. This game was probably my first real gaming disappointment.

 

[daveman247]

Assassins creed, brotherhood and revelations. Or as i like to say, the expansion packs for ac2.

Pah! You obviously meant to say that Assassin's Creed 2, Brotherhood and Revelations failed to deliver where the first Assassin's Creed got it right. The only thing the sequels had going for them were the still impressive cities and landscapes.

Cant tell if trolling or serious... Assassins 2 WAS how a sequal should be made. Better in every way to the most disappointing first. The first was all graphics, no substance.

 

[Robert Ewing]

Spore....

It had all the potential in the universe. But it's one of those very rare games that failed catastrophically in every single area it ever explored.

Even the cell stage was really sub-par. Everything about that game was destined to be an epic evolution simulator. It... Wasn't...

It was just a largely linear, faint story based, childish, shallow, short, diluted piece of shit. And I'm glad Will Wright resigned over this...

 

[The Heavy Metal Nerd]

Christ...where to begin?

Several have already been mentioned here: Brink, E.Y.E. Divine Cybermancy...but the one that makes me cry the MOST is Avalon Code...it could have been one of the GREATS.....

 

[crappingpegasus]

Totally Spore. What a waste, lol.

Also anything from Telltale lately.

Specifically the Monkey Island games.

 

[Ekit]

Dead Meets Lead. ( http://deadmeetslead.com/ ) It has a creative setting and looks really good, but the gameplay is awful.

 

[renegade7]

Spore could have been game of the year if it hadn't been so watered down.

Crackdown 2 just could have been handled a bit better.

Metroid Other M had a chance to be an awesome game with an amazing story but some piss poor design choices really ruined that.

Warhammer Online WAR could have been a great pvp fantasy experience but ended up just being another WoW clone.

 

[Jake0fTrades]

Kane and Lynch.

What I expected: Two men forced to do whatever's necessary to save their families from a heartless band of mercenaries.

What I got: An F-bomb every 2.5 seconds, clunky controls, and a really haphazard story.

 

[Bradeck]

Angry birds. I expected alot more, based off the hype. What I got was interesting for like 2 hours, then became a game of how quickly I could hit the button. Also WWF. I like scrabble, but the game was entirely broken. When someone plays TWAT for a ton of points, it's time to review the lexicon.

 

[Raika]

Wet comes immediately to mind. The concept was for an interactive love letter to the grindhouse films of the seventies. The result was... well, it was that, but the controls and graphics weren't very good.

 

[Jordan454]

Already mentioned but I have to say Alpha Protocol, all the potential was there for this to be brilliant,but the whole thing just fell flat. The game-play mechanics were awful, also all the challenge was taken out when you could get head shots round corners

To be honest I'd say a few Obsidian games I've played have this feeling about them: Star Wars Knights of the Old Republic 2, Dungeon Siege 3 etc. These games could have been amazing but there was always something dragging them down

 

[Thespian]

Brink, if Splash Damage actually carried through with their promises and claims instead of blatantly lying to everyone.

I agree except I don't think you can call it blatantly lying. More like a new IP doing it's best to innovate and biting off more than it could chew.
I did have a lot of fun with Brink but it ultimately didn't live up to it's potential.