This anime WAS the best anime at the time of its release. Back then, America really hadn't dipped into the anime market much and it was our first foray into that culture. We had nothing else to really compare it to and the uniqueness of it was what helped it come to life. At the time, it was really good.
But as of 2014 (obviously sooner, but at the time writing) I would say that while it isn't the "WORST" anime, it's clearly something I would happily label as a "BAD" anime. Or, to be less callous to it, it's "Junk Food" anime. It's anime that really has not plot or substance and has the most bare-bones story in existence to deliver mindless, nonsensical action. Other anime have copied this formula but added more story and have done SO MUCH BETTER (say what you will, but I'd say Naruto is our modern-day DBZ and I prefer that so much more than DBZ).
And there have been so many anime since then that have just done the job better. RuroKen added more story and having more authentic Japanese-cultural aspects going on. Pokemon is probably just as big, if not bigger, and continues to make NEW content every year regardless of quality but it still has an audience or it would have stopped by now. Death Note removed most of the action entirely to focus on plot and I hold it up as one of the best anime ever of all time.
DBZ is, to me, nothing but a jumping off point. Those who still love it despite the fact it really was an empty filler of a show are more than likely looking back through their rose-tinted nostalgia goggles and ignoring all the glaring issues the series had. And while I don't like the series, I greatly respect its existence because without it, it's hard to say if anime would have ever become popular in the west. Or, if it did, what shape that popularity and fandom would have taken. But ignoring the cultural significance of it and focusing on just the content of the show itself, it's not good and many shows have done it what it does, but better.