With that out of the way, 3 Idiots is a movie with the message that students should study what interests them rather than what will land them a lucrative job. If I were to describe the general theme of the movie in one word, it's: "Independent-Thinking" (yes, those were two words, but look how smartly I hyphenated them)
While watching the movie, I felt that there were two forces pulling the movie apart. One being the good part (for lack of words in my vocabulary) which showed the real deal in engineering colleges and which made me laugh. The other part being the cringe-worthy part which showed Bollywood illogic in all its charms. The good part reigned the first half of the movie. The cringe-worthy part unfortunately took us to the end.
There are jokes in the movie which have been lifted off the net. A certain part even seemed to have come from the book "The Kite Runner". So if we think about it, although the makers of the movie wanted the message of independent and original thinking to get to the audience, they themselves didn't get it completely.
Final word: watch it once. Or if you can wait, just download it off the web (legally) after 12 weeks and don't spend money on those expensive tickets.