Guys, there were a bunch of other games before this generation. Just saying...
SO... on-topic, I'd say all the final bosses in Gradius games are a joke. In Gradius 1, you get to him, you wait 5 seconds and that's it, you finished the game. In Gradius 2, just shoot his sorry face and you win. In Gradius 3, same thing. In Gradius 4, cut the limbs that are holding the head. Finally, in Gradius 5, you just shoot the eye and you're done. Oh yeah, instead of doing something in Gradius 2 to 5, you can also just wait there and the boss will kill himself just like any other in Gradius games. It's pretty funny!
As for a disappointing boss, I have to say all of Ganondorf's forms in Twilight Princess. The setting of the battle was epic, but man, could you make it more difficult next time Nintendo?
Random game thought :
Why is Bionic Commando Rearmed 2 getting so much hate? We finally get a real game and they're not even satisfied... I'm starting to hate the gaming community so f****** much...