I know that Dragon Ball Z is really popular but I don't really get the essence of this anime.
It's just too boring according to me.
IMO If you just tune it it gets really boring. Dudes talk like 20 minutes and then they fight so fast they just animate dots.
Tune in again after 100 episodes same deal different villain. It is hard to be invested without knowing the characters. The thing is that DBZ is a continue festive of taking things to the next level. After each villain they defeat a new horror comes that involves more risk than the last. All this techniques and transformations that make no sense in one seated make sense for the fans because they were slowly introduced one by one.
Dragonball introduces the characters and the archetypes of today's equivalents of this type of Anime. Luffy and Naruto took inspiration from Goku and dragonball Z universe. In retrospect yes, some episodes are dull and drags out unnecessarily but at least for me, at the time, DBZ was an adventure that pushed Goku and the rest to where we didn't imagine they could reach. If you start DBZ knowing Dragonball you will be already attached to some of the characters and their development they have had up until that point. If you care, you could try the TSR's abridged parody. It is a great way to condense in 5-10 episodes a whole season.
Anyway, not saying this to change your mind more than to explain the popularity.