It's too bad that back then the big-wigs couldn't leave well enough alone. Toriyama originally wanted to end the Dragonball series after Goku defeated Frieza, with Goku being the one and only Super Saiyan (and possibly dying when Namek blew up). However, people demanded that he continue the manga when he didn't intend to do it beforehand. So instead of having a decently thought out ideas brewing in his mind for years, he ended up recycling old ideas with different characters, and not as much pre-planning as he would have liked.
There was a break in the manga after Frieza while he thought up these ideas, but of course Anime can't take a break, so they put some filler in (Something manganime fans are suffering now in Naruto and Bleach). Hence, the Garlic Jr. saga right after Frieza is filler, while they waited for the manga to get a move on.

As for the animation, the show is very well animated in certain episodes (the important ones), especially in the Cell and Buu sagas at the end. Dragonball can't compare with the anime of today, partly because the series in general is 20 years old, and because everything that's been inspired by it has vastly improved on its formula.