Absolutely love that show, however I can see that the crude humour and cringeworthy scenarios aren't for everyone.
I'm not sure I'd agree that it hasn't aged well though, at least not in the same way that Fawlty Towers hasn't. It's intentionally offensive (in the same way that Frankie Boyle's stand-up is offensive) and I think you either find that funny or you don't. True, the main characters often insult women, the disabled, the elderly etc. but that's kind of a commentary on the mindsets and attitudes of a lot of teenage boys which I personally thought was spot on, at the time it was made at least.
The casting is brilliant as well, especially Greg Davies as the sadistic head of sixth form. Even funnier when you know he used to be a teacher for real.