Ronaldinho could do things on the pitch that no player could ever do. Messi benefits from having an amazing side, Ronaldinho had a very good team but the Barca team Messi has been a star in recent years in markedly better than the team Ronaldinho carried for a few seasons he was at his peak. Ronaldinho can change the entire game throw producing a killer unorthodox pass, dribble past a player or two, deliver a great free kick but he was at times hit or miss whereas Messi is far more consistent, a better out and out dribble he isn't very fancy but his explosiveness is something to behold.
The only player I would probably say in my lifetime that I saw, that equally amazed me the way Ronaldinho did was a PRIME Ronaldo back at Barca/Inter.