The reason that a movie needs to be comprehensible on a first viewing is simple; you have no idea whether the audience will like your film, or if they'll want to rewatch it, so the message must be put forwards the first time watching. Now, with 2001, not only do you need to watch the film multiple times, but you also need to read the book and the script notes to get the point of it all. If I don't even like the movie, what makes Kubrick think I'll want to read the book? Again, had the third act been the main premise of the film, with it's chilling depiction of an AI, some excellent (if not slightly wooden) characters, and a sense of both paranoia and isolation, this film would've been so much better. As for the cliches, this is the only place I can defend Kubrick. When this movie was released, none of the cliches in the movie were actually cliches.