Being a veteran of Terry Gilliam films, I was ready for a visual feast and flights of fancy, but once again all the imagination in the world isn't going to save you if there is no character growth or a story with characters you can care about.
As usual for Gilliam, the film, while brilliant in its cinematography, lacks focus while the characters are nothing more than pieces on Gilliam's chessboard - to be moved around, feinting here and attacking there, in attempts to support the visuals.
The main failing here as I see it, is that the character of Dr. Parnassus fails to elicit any pathos whatsoever. Here you have to potential of a tragic figure, on a level with King Lear, but Christopher Plummer plays him as a bumbling buffoon; a drunk who mourns his decisions and yet keeps repeating the same mistakes. He has every chance to become heroic, especially when he gets yet another chance at redemption and change the fate of his daughter, and yet seems oddly detached and unable to summon up the gumption to make any more than a half-hearted effort. I felt like reaching through the screen and shaking Plummer - wake up you idiot! The daughter you supposedly love needs you to step up! But no... even when what he has to achieve is so simple.
I can't really blame Plummer here, as I'm sure Gilliam scripted the character this way - leaving the major plot moving to Heath Ledger's character. Ledger is complex and interesting in what would be his last role; and I thought it very inventive how Gilliam was able to film around the loss of his lead character (inside the imaginarium, your imagination takes over, so of course it's not out of the question that your own image would change - and what a lovely surprise is in store when that happens!).
The character that really interested me however, was Mr. Nick, played by Tom Waits. He keeps winning bets from Parnassus, but then continues to offer him second and third (and 1,000th) chances. There is no profit in it for him to do so other than to continue playing the game. It's as if Nick is using Parnassus as a lab rat, just so he can watch the experiment continue to unfold.
There are scenes of true brilliance here, as when the reality created by Ledger's imagination gets assaulted by truth and begins to crack and shatter - but all these inventive scenes aren't grounded in anything to make you care about the characters - so you feel as if in a giant video game that's going to reboot regardless of whether a character lives or dies.
At film's end, a little boy asks Parnassus if there will be a happy ending - to which Parnassus replies that there are no guarantees... all as Mr. Nick smiles and suggests yet another bet. If only the possibility could have existed for Parnassus to rise above himself and defeat Nick once and for all - but I suppose that could be construed as the film's message - mankind has been blessed and has been given eternal forgiveness for our sins, and yet for all the grace we've been given we keep on sinning, and so the game continues.