Fallout 3 - Hindered by inexcusable bugginess, the lack of depth and character its predecessors had maintained, uninspired clunky shooter combat and a sorry excuse for a real-time with pause system, atrocious writing, an abysmal quest structure with awful, awful, reasoning behind idiotic administering of arbitrary karma doses (you're evil for killing a bunch of psychotic ghouls with good intent in your heart, evil for killing obviously insane bloodsucking murdering bandits in order to save an innocent town!), putrid graphics with a boring brown/teal color scheme (heads up Bethesda, for all the excuses you made about there not being appropriate technology in 1998/1997, they did have something called 'more than five colors' that you seemed to have failed to utilize), atrocious animations, useless skills, a complete lack of customization (you will eventually have the majority of your skills maxed), and worst of all, retarded NPCs that drove me fucking mad as they blocked doorways for all eternity, thank you Bethesda, for um, 'fixing' y'know, one of the original titles' most annoying problems.
Ultima 9 - Another laughable attempt at modernizing a venerable RPG series. The methods utilized here? Cut out party members (let's ignore all the complaints about Ultima 8, why don't we), insert annoying Zelda styled dungeons, terrible optimization, laughable world design with about three buildings in major cities and five residents, unbelievably buggy framework, boring forgettable combat, shitty writing and a stupid-ass plot that is both contradictory to the series' lore and is just plain terrible by any standard, and the total obliteration of what could have been a decent canonical ending to the series by a completely idiotic development team.
Deus Ex: Invisible War - Jesus freaking Christ.
movieman523: Most disappointing for me would probably be Deus Ex; I gave up half-way through the first level and didn't go back to it for a couple of years. But then I was playing it a few years after it was released, so it was probably far less impressive than it would have been at the time.
Common mistake, that first level is typically considering a putrid stink hole, and for good reason, it sucks. It's just a glorified tutorial mission and as such it's just an uninspired collection of 'options' meant to familiarize you with the game without actually telling you it's a tutorial, so it gives a false impression about the rest of the game.
Getting through that missions opens up the rest of the game which is pretty banging, the game doesn't have the most engaging combat, but it's a lot like the original Fallout games where the fun comes from manipulating all the various options available to you and simply messing with game itself.
