I wouldn't say I was disappointed by FF7 but I do think its a little overrated. I've only played 7 on PSX and 4, 5 and 6 on the SNES but I much preferred the SNES titles. 7's graphics are ugly, the game plays a lot slower, and materia makes the game grindier.
I was disappointed with Bioshock. I loved System Shock 1 and 2 and when Bioshock was billed as the spritual successor I was disappointed to find that it was dumbed down into basically a fairly standard shooter with an admittedly unique setting. The RPG elements had all been removed, the big plot twist was phoned in (if you'd played SS2 you'd have seen it coming a mile away).
Mass Effect 2 was disappointing. For all its flaws I really liked the first one, I liked the idea of having a space ship that you could land on different planets and explore them. Admittedly the game felt unfinished, most of those planets were empty, if you just followed the main quest you probably could finish the game in a couple of hours (most of that time was spent in dialogue trees). I was hoping they would expand on the exploration and RPG elements in the sequel but they actually took most of that out, now you just 'scanned' planets instead of exploring them, the game basically just alternated between conversation and combat.
I didn't even bother with ME3 but from all the rage on the internet it appears the ending is really disappointing.
Battlezone 2, I loved the first one, being set in the cold war, yanks vs commies.... the second one just seemed to lack that special character. I played the first over and over but just couldn't get into the second.
Civilization 4: Colonization... again, loved the original, the remake was dumbed down, a lot of the features, terrain types and cargo types were removed. I've heard there are mods to make it more like the original gameplay but I haven't bothered to look into this further.
Duke Nukem Forever... I grew up playing DN1 and DN2 shareware, my PC at the time wouldn't run DN3D but a friends did and I wasted many hours over there playing it. Read the previews at the end of the 90's hyping it up, it looked awesome... we get it a decade later and it sucks. Broussard fucked it up, kept fiddling with it, chopping and changing as he pleased, we ended up with a COD clone. That whole alien hive level was boring and offensive and would have been better off if it wasn't included in the game. They should have released it 10 years ago when Duke 3D was still a badass, now he just seems like a try hard.
Oblivion (and to a lesser extent Skyrim) - I loved Morrowind, had cool setting, unique flora and fauna, the sense of exploration was awesome (didn't have a compass telling you where to go) and given that more items were hand placed rather than randomly generated the reward for exploration far outweighed the risk. The plot was cool and levelling up to become basically a superhuman was cool. Oblivion sucked, had a generic fantasy setting, stupid level scaling that made the game impossibly hard if you put most used skills as primary, (enemies would become damage sponges and combat became a boring battle of attrition). You'd explore a cavern or dungeon and come out with 3 septims and a spool of cotton. The plot sucked too, you weren't the hero, martin was. Features like levitate were removed because it was too hard for them to make it work without breaking the game.
Skyrim improved on oblivion a lot but still it felt a bit like the risk/reward of exploration wasn't as good as morrowind's. They added a lot of stupid features like smithing that just encouraged grinding for levels. The exploration felt a bit samey after a while; you'd slog through a long dungeon that looked the same as all the others, solve an insultingly easy puzzle with those symbols, fight a boss, get a few coins and maybe a shout, and then get shown a convenient exit that takes you right to the front door again. I really think that they've lost sight of what made Morrowind great, it was a rich, deep experience, but I feel the sequels are broad but not deep.
If you are squeamish, don't prod the beach rubble.
