Even though the final season was rather slow, and glossed over a lot of plot lines that probably would have been more interesting, it was still better than most science fiction, and any on television other than the earlier seasons. Other than the final season and scattered weak episodes, the series is the best television science fiction, and near the best dramatic television, and competes with the best movie science fiction.
The action in the series is mostly about the Shadow war, but the real key is the intrigue between the characters, and the personal growth of the characters. Londo is one of the best dramatic characters in any series. He starts as an ambitious schemer who drinks too much, but develops a conscience as he learns the consequences of his ambitions, and finally ends up as a tragic character who reached even beyond his early ambitions, but at a cost that he regrets deeply.
Maybe some day there will be a better science fiction series. But for now this is the level of story-telling television science fiction should try to reach.