What I liked most about the series was how well planned it was. The first episode is almost entirely foreshadowing of events that happened later. Contrast that with something like the newer Battlestar Galactica.
To be fair the fifth season wasn't as good as the first four. Whether you chalk that up to JMS holding stuff back for Crusade, TNT interference, JMS getting tired after five years or simply a poor story. I was expecting something amazing to finish the show but it was just lackluster.
Galactica, while obviously making it up as they went along, had a great ending.