Yes. I was not impressed and would never recommend it.
While some people (who I do not profess to understand) might find it humorous, beyond that it has no redeeming qualities. Not really wonderful Christian material, either. Numerous sexual references, nudity, etc. Because I do not like the manga very much, I have little else to say about it.
I would I loved it, I have the live action series, movie, and anime, plus the manga that they have released so far, I wish I would have had a teacher like that when I was in school, I definately recommend it. May not be for kids though.
Anyway, I personally liked it, but as UC said, it's definitely not good in terms of Christian values. If you liked titles like Psychometer Eiji then GTO would be your choice (they both got similiar art and comedic styles).
-Psalm 27:1-
The Project - Online Christian manga, rambling FAQs, and Truly Random Scripture.
Cognatio- Online Christian Manga Exchange