It started decent, and turned bad over time, like many shows.

Yeah to be honest I found season 1 Jake more annoying because of the overuse of street slang (it was done in such a "trying to seem hip to the kids" kind of way that it bugged me), but the other seasons really toned it down.

Also the change to Jake's dragon form was actually kinda interesting when you think about it. Jake's of a mixed Chinese and white-American ancestry, so it's like season 1 his dragon form took more after his dad's side (many white people being of European descent), but from season 2 and onward it was a much thinner dragon looking more like the ones from Chinese mythology.