I agree with Darkling that his introduction is rather good, but after that...well, he doesn't do anything useful. He is loud and it's a wonder nobody heard him talking about the escape plan. And after the escape from Efrafa, he doesn't get a single line. He can be seen on occasion, generally during meetings, but never does anything useful.
Another thing I found annoying is that he isn't even black. There was a reason why he was called Blackavar in the book.
Am I the only one who thinks he was killed during the battle in the caverns? He isn't seen or mentionned afterwards, as far as I know, and just before the battle, Hazel told Bigwig (?) to get a few rabbits, him included.