I haven't seen the film, but I've read the book countless times.
My favourite character probably is Yossarian, but I don't think I've read a book with so many colourful characters.
My favourite scene is probably the pre-mission briefing with the 'moaning' incident. The moaning reaches a crescendo before being silenced, and then one of the staff unintentionally moans. The CO then orders him shot.
The most disturbing part of the book is Milo and his business. How he bombs his squadron using USAAF planes on contract from the LW - funny, but a little bit weird.
If you are expecting anything on a par with Catch-22, don't read the sequel 'Closing Time'. But then Heller himself admits he could never equal Catch 22.