The score of 6 let me think that Zetman will be bad, but it definetly deserve a 7 or a 8.
This anime is good, you got old scientist who creating dangerous creature which run out of control, a main character with badass hidden hability, almost authentic love story ( without annoying fan service, women are not over-sexualise by other character) and some rage moment wich are pretty satisfying. The story, as you could gess, is pretty generic ( like tokyo ghoul, kiseiju and a bit like devilman ) but it's coherent and the animation is relevant (better than lot of crap 2D or 3D animation which have higer score *humm first episode of kingdom* ). The story-line doesn't spend time in boring explanation, action are promptly coordonate and there are a lot of explanation explane by camera angle or expression of character.
The last episode isn't good as the rest of the show but eventually the anime derseve a better score, i 've spend a good time and i was hype by the progression of the MC.
Try the first two episode and don't let the score influence your opinion