O'Hare's departure from the series was noted by creator J. Michael Straczynski to be "mutual" and "amicable." Thinking back, while O'Hare's Sinclair was not my favorite character on the series, some of his work for Babylon 5 is notable and highlights from Season One starring O'Hare include Episode 8, And The Sky Full Of Stars, Episode 13, Signs And Portents, Episode 20, Babylon Squared and Episode 22, Chrysalis [three of the four episodes noted as the best in SciFiNow's Best Of Babylon 5 and Ten Of The Best]. One of the very best of the entire series is Season Three, Episode 16 & 17, War Without End Parts I & II as noted in the Sci-Fi Fanatic BIG 10: Babylon 5.
There isn't much specific coverage out there regarding O'Hare's quality entries as leader of the Babylon 5 space station and universe that first season when there are plenty certainly worth consideration. Michael O'Hare passed away on September 28, 2012. He was just 60 years of age. May your star fill the heavens indeed.