One reason why I think a lot of Amercian fans turned on it was because the Buu Saga re-introduced comedy back into the series in a pronounced manner, which I think was off-putting to many American fans who were only familiar with Z and not Dragon Ball, and this included me when I was younger. It didn't help that a lot of it came from Buu or Goten and Trunks, characters I use to find more annoying than funny. Like, Goten and Trunks turning into a Super Saiyan so young is essentially a joke, and that use to rub me the wrong way. Now, I just find it funny, and works as a nice nod to how easily Goku use to pick up on sacred techniques like the Kamehameha (besides, the Super Saiyan legend was already kinda tarnished with how many characters achieved it during Cell and I can believe that Super Saiyan semen makes it easier for the offspring to achieve it). When I was younger, I remember really being disappointed with the arc. I loved most of the beginning bits, but felt the arc peaked with Vegeta's sacrifice, and the rest was a disappointing follow up with some cool moments like Candy Vegito or Gohan's "I'm here to kill you", though Gohan's poor performance further sullied the arc for me. Which is another problem most people had with Buu, it fails to follow up the passing of the torch moment in the Cell arc.
Having earlier this year read the manga fully for the first time, I came away with a much stronger appreciation for Buu. I think it's probably thematically the strongest arc in Dragon Ball, most of the humour really did work for me, the end of the arc is great. And despite how neutered the cast was at this point, there were still little things I appreciated, like showing that Tien survived the attack the wiped out humanity or Piccolo's biding time for Goten and Trunks with Super Buu. But yeah, I did have an issue with how neutered the cast was, and I also had a problem with how back and forth the action got against Buu. The good guys would get a power up and start dominating, things would change and Buu would start dominating, then the good guys again, then Buu, it just become a slog where dramatic weight was meaningless because this deck was full of Uno Reverse cards.