I recently re-read the entirety of Dragonball. That's right, all 42 volumes of it. I first read it not so long ago, maybe a couple of years ago, but it never ceases to amaze me just how different in tone the later volumes are to the earlier ones. Personally, I much prefer the humourous fantasy that so characterised the first part. As soon as it hits what the translations call DBZ it starts to go downhill. Don't get me wrong, I still love it, but it does start to take itself far too seriously.
I'm fairly certain that Toriyama wanted to quit writing it long before he actually did. Look at all the chances he gave himself to stop writing:
1. He could have finished with the end of the Piccolo Jr. Arc. Goku has become the most powerful on Earth. The demon Piccolo is still a threat, but we know that he can't really beat Goku, so all is well.
2. He could have finished at the end of the Frieza Arc. Goku has beaten Frieza, the most powerful being in the universe. Piccolo, having re-discovered his Namek heritage, is more or less a good-guy. Even Vegeta probably won't try anything too evil, so all is well.
3. He could have finished at the end of the Cell Arc. Goku is dead, and wishes to remain so. His story has come full circle. Rising to become the Earth's defender, and then passing on the torch. Gohan has assumed his duties as protector of the Earth. With Piccolo, Vegeta and Gohan protecting the Earth, all is well.
The absolute absurdity of the Buu Arc (Gohan goes to school! The entire population gets turned into chocolate! The fusion dance!) suggests very strongly a kind of 'I'm gettting tired of this, I want to end it and try something new' thought chain from Toriyama. Any of the aforementioned points would have been excellent ending points, and if I bet Toriyama would have been happy ending the series at any of them. So why didn't he? In a word, money. Dragonball was a cash cow for Shonen Jump, and they didn't want him to stop writing it.
Don't get me wrong, I love the Buu Arc. It's wackiness is remeniscent of the early volumes of the manga. I love all of the characters introduced in it: Videl, Goten, Trunks, Vegito (Yeah, yeah he's a fusion I know, but he's almost certainly the most powerful being in all of the Dragonverse including the awfulness that was GT. He's even the World's strongest coffee candy!). I love that the Earth is finally given the oppurtunity to save itself and almost turns it down.
However, I hate the idea that Toriyama might have burned himself out writing Dragonball. He is a very talented artist, and I first came across his work seeing the character designs for the legendary Chrono Trigger (Yeah, that was him).
Anyway, I guess the main point of this is that, even now, I still love Dragonball.