Buu was kinda disappointing for me. I had built up so much about what he was going to be like.. and it wasn't all that great. :( But that's just my opinion.. :P
The whole point of Dragon Ball Z was to pass down the reign to Gohan. I loved how Goku took a backseat in the Cell saga and said "Gohan, you're going to have to do this someday, you might as well start now." However, the fans didn't like Goku stepping down... so AT decided to milk the Buu Sagas pretty much. Gohan became the most powerful in the universe when he became Mystic, only to have to be bailed out by his dad. Bleh, Buu Saga was so sloppy and it was getting towards that GT mentality of "Goku has to do everything." After the Cell Saga is disappointing, mainly because of Gohan.
Piccolo: When Nappa did that attack at Gohan why did he just stand there? He could have just ran in there and grabbed him while he was running by him. But I think that attack was going much much faster than what it was shown.
Mecha Frieza and King Cold: I know the whole Frieza thing had a shit load of episodes, but they could have at least had that battle last either a full episode or two. (I just hate how Trunks god-stomped them so easily.) Full powered Frieza and Trunks could have been going at it while King Cold is fighting the rest of them. Both Trunks and Frieza can be evenly match, but Trunks best him due to better techniques. Then he can kill King Cold the same way he did. After that everything happens how it did.
Fusion Reborn: Frieza: Even though Gohan killed Super Perfect Cell who was much much stronger than what Frieza was. He still thought he was able to kill Gohan.
Trunks: Future Trunks was so cool to me. Then you had Trunks and also Goten who turned Super Saiyan into a child's plaything.
That whole GT thing in Hell where you had Cell/Frieza fighting Goku.
Sakura-san Y_Y weak just weak.
Frieza's dad.... He just showed up like a boss then Trunks wiped the floor with him, hah. I guess that's just a testament to Trunks' awesome-ness
anyone who is not me. Except Holo...and Souske Sagara...and Vash... and Ed... actually, i guess theres a pretty big list of not disappointing characters lol
Nothing comes to my mind but lets see.... characters from Toradora,Saya Otonashi from Blood+ (last episodes ruined it all ) hmm that all i can come up with by now
Sadly the character that disappointed me was Gohan. He was a total badass when he was a kid and especially when he fought and killed Cell as a SSJ2. Then from the end of Cell to the Buu saga they made him into a weakling that couldn't even tap into his true power anymore and GT went on to further make a weakling out of Gohan. I know he should have easily defeated both Buu in DBZ and even Baby in GT.
Everyone in Dragonballz Z who let them get away with ripping off Superman, Back to the future, and the Terminator.
For a first serious challenge that kicked off a series, Raditz was pretty disappointing.
I've always felt that everyone became a disappointment by around episode 200. Vegeta sold his soul to the devil ('s pet cricket) just because he wanted to fight Goku... who'd be back for only a day. God!... Literally. Why were the Gods weaker than these physical beings? Why was it that, by the Buu saga, you had to be born a certain race to be competent? No Fem-Super Saiyans? Really? Because Mr. Toriyama doesn't think that a women with any more than .001 muscle mass per body weight should be allowed on panel? I love how Android 18 goes from bad-ass Super Saiyan killer to a household mother even in the face of danger.
Goten and Trunks were also disappointed... They felt like they were going to grow up to be great warriors. Except... They didn't. And they screwed Goten out of his "One of the Son family's men takes down the Big Bad." I guess Bio-Broly counts, but dear god, Bio-Broly. What was that?!
Most of all, Goku. He had the chance, man, to prevent people from dyin'. They could have destroyed the Androids then and there, used the Dragon Balls to find their location... But no. He and Vegeta (wait, wouldn't that be Vegeta and he? Damn my Inner Grammar Nazi...) just had to fight. Sure, it probably saved them in the longest run (even though Babadi probably would have passed up their planet), but still...