I saw this last year when the broadcast it at the movie theatres, and it was amazing. In the National Theatre live performances, Benedict Cumberbatch and Jonny Lee Miller alternate the roles of Victor and The Creature -- the version I saw had Cumberbath as Victor and Miller as The Creature.
But I just spotted that not only are they doing some repeat broadcasts in June, they're going to be showing both versions! The schedule for Cineplex in Canada is June 14 and 16: Benedict Cumberbatch (the Creature), Jonny Lee Miller (Victor Frankenstein), and June 21 and 23: Jonny Lee Miller (the Creature), Benedict Cumberbatch (Victor Frankenstein). I would imagine the schedule is the same for the theatres carrying it in the US.
More info and venues worldwide.