GTO: 1-29 (re-watched 1-20)
With episode 20 out of the way, SP started doing what they do worst: filler. They added some crappy back-story to Azusa to extend an excellent single chapter into two episodes, ruining it in the process; they had Onizuka teach Uchi's daughter and Uchi take on the riot police in an ape costume and, in order to extend a side-story section of the manga and get the main character in the picture (like in Naruto), they inserted Onizuka and some random students into Tomoko's once amusing story, also extending it by repeating the Tomoko contest drama of old.
And, maybe even worse, there was a two episode filler arc which borrowed a character from the prequel manga, SP made Onizuka/Ryuji not know her and repeated her story from the prequel. Isn't this sort of thing known as 'retcon', or something?
It's a shame because, though I wasn't fond of the adaptation originally, I warmed to the first 20 episodes of the anime when I went through them without a clear image of the manga in my mind. But SP have worked their filler magic and made me 7/10 it. :/
On the plus side, the manga story got going again in 28 with the start of the school trip arc. I'm sure the 'original story' ending will be terrible be the next lot of episodes should be great.