Dragon Ball Z is without a doubt the best anime I've ever seen. It's the anime with the greatest amount of characters that I like, it has really good villains and they are remarkable for those who watch. The fights are great and there's nothing to complain about, however for those looking for an anime with a predefined story from the beginning, DBZ is not the right choice, because the only objective there is to become the strongest and protect your family and friends, and that may not please some people.
Other bad parts of the anime are the fillers, which the vast majority are quite boring and make you lose the desire to keep watching at certain times.