I don't like to use the word 'masterpiece'...but it wouldn't be an insane adjective to use to describe Gantz. This is one of the best all around anime I've ever seen.
It has an extremely interesting and rather unique concept that is thoroughly explored and discussed through the characters. It has the surface level 'low brow' entertainment like extreme amounts of violence and a pretty hefty amount of nudity. It does an excellent job of going against the typical story clichés. Moments of character empowerment are shot down in the flash, people who seem like throwaway characters come back later, and none of the characters are safe from harm.
Speaking of the characters, they are very dynamic and what makes this show last. Good guy heroes often come off as cowardly, douchebags save the day, etc etc. The characters also come across plenty of moral dilemmas and have plenty of discussions about the nature of society.
Some say they hate the ending, or that it is confusing. I don't see why, if you just pay attention a little bit to the visuals and how the fundamentals of the whole thing works...it's quite clear. Yes, there are some things that aren't fully explained...but the end result, what happens to our hero(and/or heroes) is quite clear.
In conclusion, it's an anime with a great concept, great characters to explore it, great animation, a ton of violence, plenty of nudity, a decent amount of action and some good social commentary. Regardless of the manga, if you've read it or what you think of it, Gantz is a fantastic stand alone anime...and I think I'd prefer THAT to a seemingly endless story.
