The character development in B5 was fantastic.
Also in this series, actions do have consequences and you don't always get the ticker tape parade, and sometimes you don't get to walk away from the consequences.
Londo and G'Kar especially will evolve over the series. While they both have comedic moments, trust me they both get VERY serious as well. Just wait for the ep in Season 2 where they are trapped in the elevator.
As to Sinclair, yes the actor was very ill and did what he could to film his scenes but behind the scenes there was a lot of tension. Only he and JMS really knew and they were pals so JMS promised that he would keep the secret unless/until the actor died, then per his request he would reveal the truth, which he one day did:
Acute Paranoid Scizophrenia and the medication wasn't helped by the demands of the shooting of the series.
Sinclair will appear in Season 2 and his story arc wraps in Season 3.
Delenn will undergo a major change.
Kosh and the Vorlons get revealed as does the major enemy.
Marcus will join the show
Bester the Psi-cop will return, he is the "Q" of the series as in the character you hate and want to see dead but want him to keep coming back.
After you finish all 5 seasons, go read the B5 Novels, Psi Corp trilogy and the Wheel of Fire Trilogy
Yeah beginning with the second season everything really gets interesting. However the pilot and first season do have some good episodes are decent and has things that are necessary to the overall understanding of the series. I applaud JMS for his actions with Michael O'Hare. I liked most of the related movies as well. The show looks a bit dated and the cgi especially. The lack of money for wardrobe and set design probably will hurt for a modern audience. Never the less I loved it and recommend B5 to people. I consider it to be slightly above STDS9.