I particularly liked Mickey Rourke's bass rumbling, almost incoherent baddie! He seemed to be having great fun being as dastardly as possible! Stephen Dorff also seemed to fit perfectly into the cocky wisecracking sidekick role! I wasn't too sure about Henry Cavill's Theseus (despite looking uncannily like a young Olivier in some shots, the big rousing the troops speech unfortunately felt a little underwhelming), although the callow quality may be due to the character being a rather one dimensional hero figure getting railroaded by destiny towards becoming a mythical figure.
I particularly liked the Theseus slaying the Minotaur sequence which, in the image of the bull mask made out of barbed wire through which you can see glimpses of eyes underneath (the mask intimidating by acting both as a weapon and a cage), felt as if it were picking up some cues from that production of Harrison Birtwistle's The Minotaur. Although The Minotaur does not really get humanised as such in Immortals, though he does get an amusing sequence where the character is tracking our heroes by following the clues they have left behind, private detective style!
There is also a nice staging of the 'labyrinth' with Theseus following his wet footprints back out of the tomb. This whole sequence of interring the mother, finding the bow and fighting the minotaur is where the film is really flying at its highest. However throughout there is always, as can be expected in a Tarsem film, something visually impressive going on. I'll finish with a couple of great images from the film:


