Yeah, it's pretty fun.
Like, a lot of the game's internal humour comes from the fact that it is very literally a GTA game set in a high school, with gangs replaced by cliques and the vaguely unlikable criminal protagonist replaced by a vaguely unlikable kid with behavioural issues (although, as mentioned, he does grow on you a bit which is more than I can say of any GTA protagonist). In that sense, how much you enjoy it is probably going to depend a bit on how much you can get into that slightly tongue in cheek headspace and view the "flaws" in the gameplay and narrative as charming rather than obnoxious.
The only negative point I would really bring up is OMG minigames.. If you don't like minigames, you may find this one annoying (although again, I'm pretty sure the minigames are supposed to be a bit annoying as most of them represent school classes, see above as to whether this counts as an excuse for you, it worked on me).