I had some trouble with Commander Kruge. Christopher Lloyd's voice and mannerisms are so distinctive that I couldn't see Kruge as a Klingon. He really was just a guy in makeup and costume. Whenever he spoke or did anything, it was Doc Brown, or Judge Doom, or even Jim Ignatowski, who are really all the same character anyway. Kruge couldn't be them and be threatening.
When he and Kirk finally fight as the planet is crumbling and he shouts "Give me Genesis!" I was laughing. Kirk was fighting Doc Brown in makeup and a costume.