Occasionally a game has a last boss that has you going "What? That's it?"
Actually it happens quite a lot, but if the game is pretty damn good, that makes it somewhat worse. So I've only used last bosses from games that I find to be otherwise excellent.
Game: Lufia II: Rise of the Sinestrals
System: Super NES
If you can get to Daos, you can beat him. There really is no question whatsoever. Sure you gotta fight Gades, Amon and Erim/Lufia first but this guy is just a wuss. He doesn't really have anything special to hit you with and with well placed IP attacks he'll be dead before you could get your box of tissues ready for the ending.
Game: Super Mario 64
System: Nintendo 64
Bowser is the only character to be on both my most epic list and my most disappointing list. Super Mario 64 didn't really have anything in the way of boss battles, which is kind of pathetic when you really stop and look at it. The first two times you fight him, he's a one-hit-wonder. For the big final showdown you gotta hit him three times. Fucking pathetic.
3. Dracula Wraith
Game: CastleVania II: Simon's Quest
Simon's Quest also wasn't really much for bosses and the Dracula Wraith really is pathetic. You can whip him over and over, you can use the sacred flame or if you really want to embarrass this asshole, use the golden knife to kill him before he can even move. Dracula Wraith showed up again (with a similar concept behind it) to dog Simon's grandson Juste, but at least that time it sort of put up a fight.
4. Dagoth Ur
Game: The Elder Scrolls III: Morrowind
System: PC, X-Box
Obviously there's so much to Morrowind that doesn't involve the battle with Dagoth Ur, but I do have to point out how easy he is. In the second phase you don't even have to pay attention to him, just skip on down to the heart and hit it with Keening and Sunder to end the game. There were plenty of absolutely epic battles in Morrowind, too bad Dagoth Ur wasn't one of them.
5. The Icon of Sin
Game: Doom II, Final Doom
System: PC, Playstation, Game Boy Advance
The Icon of Sin is an interesting idea. The part you need to attack is inside of it (John Romero's head on a stick) and you can't access it normally. You shoot rockets into a hole and the splash damage hits the head, after a few rockets it dies. Honestly once you figure this out, you can kill it in seconds every time. Maybe this seemed pretty cool when Doom II was fresh but the fact that it was used again in both Final Doom episodes bothers me.
6. The Cyberdemon
Game: Doom 3
System: PC, X-Box
The Doom 3 version of the Cyberdemon seems really awesome and intimidating until you actually fight it. You can't hurt it, only the soul cube hurts it, so you spend the battle staying the fuck away from it, where he can't even hit you as long as you're moving, and kill enough minor enemies to charge the soul cube, then send the cube at him, (you barely even need to aim) and he dies after a few shots. Sure he can kill you by walking over you, but for what reason would you ever go near him?
Game: Mega Man X6
Sigma appears at the end of each Mega Man X game and is the end boss in every one except X8. He really shouldn't have bothered showing up for X6, because it's on the back of a great battle with Gate, and then Sigma shows up all fucked up, he can barely talk, and is clearly not at full power. He goes down easier than a Saigon whore and then you get the ending. The game is great, but the Sigma battle is just a joke.
8. Alec Trevalyan
Game: GoldenEye 007
System: Nintendo 64
Urgh. A great game slightly marred by the lack of any real bosses to speak of. Alec is in the last stage where you gotta shut off a machine and then chase him around the level shooting him in the back. He doesn't even fight back for the most part. When you've done enough damage he goes down to the bottom of the cradle and just stands there waiting for you to shoot him. He usually at least dies in a dramatic fashion, falling off the cradle, but sometimes he just drops like any other enemy in the game. You don't even get to see the satellite fall on him like in the movie.
Game: Star Fox Adventures
Talk about taked on. The battle with General Scales ends early so they could shoehorn Andross into the game. So back in the arwing for the same old shit, just avoid his shots, wait for Falco to give you a bomb and hit him. Rinse, wash, repeat, vomit.
System: PC, Nintendo 64, Playstation
You Telefrag it.