The Imaginarium of Doctor Parnassus is a Terry Gilliam movie. It's beautiful and it's weird and it has big, broad ideas that don't really work out to a very sensible or well-plotted story. All the actors do great work, though their characters, toward the end, start doing a bunch of shit that doesn't make any sense. Tom Waits as the devil is a highlight, but Verne Troyer, surprisingly enough, turns out to be a good actor, and newcomer Lily Cole is more than just an incredibly gorgeous face.
My favorite bit is like a CG version of Gilliam's old animated Monty Python segments. Seriously.
Everything to be said about how Ledger's death hangs over the film has been covered in every single review of the film already. There are a couple of scenes that are eerie or disturbing in this context, and I think they work well for it without crossing over into being maudlin or exploitative. Ledger does decent work; not his best but quite good. His three doppelgangers do an admirable job of playing his character; I think I like Depp's portrayal best but I think Farrell does the best job of mirroring Ledger.
...mirroring. No pun intended. Really.