I will miss him greatly.
He was my favorite character in B5. I really liked Bruce Boxleitner, but I loved Michael O'Hare.
He had a quiet yet at the same time strong manner to his enactment of Commander Sinclair. I watched B5 in their first airings and own the entire DVD set plus all the movies. I can't tell you how bummed I was when the 2nd season had Sheridan as the new Commander. Once again, I really liked Sheridan a lot but whether J. Michael Strazcynski purposely wrote out Sinclair or whatever... there was nothing wrong with the first Commander... please bring him back!
He was only 60 years old... way too young. May he rest in peace and he will be remembered.