It isn't really much an adaptation of DBZ so much as it is "INSPIRED BY THE WORKS OF AKIRA TORIYAMA!" They got some of the character names correct, and then made up the rest.
Funnily enough, I was STILL willing to give this movie a chance until I saw Piccolo. Wait, don't tell me, he isn't even an ALIEN, he's just some kind of terrestrial monster.
I mean, I can understand them not including the likes of Oolong and Puar, and EVEN gave them the benefit of the doubt when they said that Krillin wouldn't be appearing, because sometimes characters just don't belong in a specific story, and Oolong and Puar would have been some seriously budget-draining CGI.
But come on. Piccolo is an ALIEN, and he's GREEN. I don't mind if he's the bad guy of the movie, because Piccolo was Goku's enemy for a while. But come on. If he's not green and an alien, he isn't Piccolo at all.