Gimli is the MAN, by all accounts. True, he was somewhat underplayed in the movie, but that was the director's decision. John Rhys-Davies is the man, too, and he played Gimli so unbelievably well.
But one thing that I just realized is that, in the movie, after the Council of Elrond, they never really showed much distrust between Legolas and Gimli. I would have liked to watch their characters develop a little more, but hey, you don't get everything in a movie that you get in a book.
One other thing that I wished I could have seen was Gimli taking 10 orcs at once on his own, or something like that. It would have been nasty to see him plowing down tons of orcs at a time. Unfortunately, in the Two Towers, when such a moment was possible, he falls in a puddle. A very disappointing moment for me.
It's just that they gave Legolas and Aragorn their moments of glory, but Gimli went very unappreciated throughout the trilogy, when it is likely that he is the most steadfast of the three of them. And Boromir, too, got his moment of glory, which surpassed awesome. But they left Gimli out. I don't think it's very fair, but hey... What'ya gonna do?