Been watching B5 with the missus and we've made it a fair chunk of the way through the 2nd series. Sadly Naomi agrees with me that there is no subtely in the way in which Michael O'Hare is replaced with Bruce Boxleitner. A lot of folk diss O'Hare as being at times wooden, including certain co-stars but I felt he needed to be in the first few episodes of season 2 at least to transition from one CO to another.
It does seem for a few episodes that Sheridan is walking around being really nice to people for no apparent reason, and that no-one is resentful that poor Sinclair got transferred finally. For Naomi though the point where the obvious tipexing of Sinclair with Sheridan hit home was in episode 2 of season 2 when Captain Sheridan volunteers to give some of his life-energy to save Garibaldi. This doesn't really work from a dramatic point of view as Sheridan has never met Garibaldi, while it would make sense for Sinclair to do so.
Still one does wonder how the show would've been with Sinclair... probably not as good if this account is accurate. Though I think this was probably just the rough draft of Seasons 1-5.