Providing the characters with an episode to discuss their issues with each other and come to decisions, "'Til Death" doesn't do much to advance the storylines but lays the foundation for the episodes to come.
Sisko gets the weightiest matter, with his heart telling him to marry Kasidy and the prophets saying otherwise. The subject matter plays to Brooks's strengths, with Sisko having an internal struggle; unsure what the right choice is to make... or if there even is one.
Meanwhile, Worf and Ezri spend the episode in a Breen holding cell, giving them plenty of opportunity to continue their bickering in a repetitive plot line that doesn't really go anywhere but circles. The idea works for "Waiting for Godot" because the circular nature of the story includes subtle variations to sustain interest. Here, however, it's just a stall that draws attention to the fact that these two characters have no chemistry together.
As for the "evil forces", the Dominion continues to plot (giving Jeffrey Combs an opportunity to steal a scene) but isn't yet in position to press the Federation. The most perverse (and interesting) plotline, however, sees Dukat, disguised as a Bajoran, courting Kai Winn and winning her heart (appropriately enough) through falsehoods. Proving the DS9 writers are a sick, twisted bunch (which is great, by the way), the sequence of scenes between the two just gets creepier and creepier as it moves along. Still, DS9 gets ahead of itself with this particular thread, starting up the Dukat/Winn stuff (by their admission) too soon, leading to some stalling in later episodes. Looking back, "Penumbra" and "'Til Death" would be better if they were combined into one fast moving episode focusing on Sisko, with the Dukat/Winn situation postponed for later. As is, "'Til Death" is sort of like sitting in a waiting room.