I read on wiki that RDJ is a big fan of martial arts. +1 to himAgreed 100%. They should have turned up the notch on Lord Blackwood a little. He was a good villain but like you said, fell just short of true arch nemesis status.He was a little too behind the scenes, so you couldn't fully appreciate how devious he was in setting all those traps and pit falls for Sherlock and the other lords.
The man's nationality should not be an issue, seriously guys, he's an actor, that's what they do, pretend to be other people. Was Gerard Butler's role as Leonidas (spartan) in 300 any less convincing because he was Scottish? How About Mel Gibson as William Wallace (scottish)? or maybe Russel Crowe as Jim Braddock (american)? Complaining about casting people with varying nationalities boils down b!tching at the end of the day, what you should ask yourself is; Can Robert Downey Jr carry this role convincingly and successfully?RDj is an actor, and an exceptional one at that, and that's enough for me.