Ali G used to be a fantastic concept. The character originally used to interview MPs, church leaders, prominent figures. Managing to outwit and highlight the ignorance within these people about street culture. It was very funny indeed. These people Ali interviewed seemed unaware of the joke!
A year or two down the line, more money was pumped into the character and the scripts expanded, along with Ali's head. He became (as has been already mentioned) a larger than life white kid (although he looks Asian to me) who claimed to be from the ghetto and had his own TV show, which for the most part was an excuse to be sexually perverse, glamorize drug culture and gangsta lifestyle. Which was fine for the first series in a way, as it was quite funny in parts and the interviews continued but this time mostly with media stars who were in on the joke.
To me, the joke has grown stale and the latest series and indeed the film (now out on DVD) you can have compressed into around half an hours decent material, the rest being garbage.
Ali should be put to rest or at the very least, grow up and evolve into a slightly more mature version of the same character.
Personally I wouldn't let kids see the show, as it is pure satire, but they won't appreciate that fact.