You really have to see some of Carrey's dramatic films as well (and not just Truman Show); the guy is talented.
Also; I saw some interviews he did on Australian TV, and the guy is genuinely spontaneously witty, which is something that's not common among actors when they're not working from a script.
He told a great anecdote in one of his Australian interviews in regard to his gurning.
When he was young, he used to spend hours pulling faces into the mirror, and his mother told him, 'Stop doing that, or you'll see the Devil!'. Of course, the thought that he had in response to that was, 'Where
is the Devil? I want
to see him!', and that encouraged him to do it more than ever.