Yeah, just to echo to what everyone else is saying--Context. Matters.
Also, with B5 you should always remember what G'Kar said to Sakai way back in 'Mind War': "No one here is exactly what he appears. Not Mollari, not Delenn, not Sinclair .. and not me."
True to form, by this point in the show we know who and what Sinclair & Delenn turned out to be and now we get to begin to find out who Londo and G'Kar really are.
As for Sinclair's changed manner, yes, he is more at peace and no longer haunted by his past as he once was. A lot happened to him on Minbar, a story which incidentally is told in the canon novel 'To Dream in the City of Sorrows'
. For a tie-in novel it's pretty good. Basically, it follows Sinclair, Sakai & Marcus from around the start of season two, up until the start of season 3, showing how the Rangers were revitalized from an ancient relic of an order--a quite embarrassment to the warrior caste, mostly made up of a scant handful of old men, only kept around only out of respect for it's history--into the effective fighting force we see on the show.