There are so many things that happen in season 5 that I hardly know where to begin! I remembered a lot more of these episodes than I did the earlier ones, but then again, I was a lot older when these aired than I was when season 1 aired! So I probably saw more of them, and I know that several of these episodes were frequently replayed as well.
Season 5 has some entertaining love stories. Quark tries to woo his Klingon ex-wife, the O'Brien's and Kira have some interesting dynamics in the their relationships as Kira carries their baby, Quark's Mom starts dating the Grand Nagus, and even Odo has a romantic interest in one episode! Of course the best romance, in my opinion, is the developing relationship between Worf and Dax. By the end of the third episode they have finally moved beyond friendship to passionate love (involving many broken bones and bruises), and we get to watch them date over the rest of the season!
We also have what is probably the most famous episode of the entire show in this season, "Trials and Tribble-ations." This was the 100th episode for DS9 and the writers wanted to do something special. They had several different (and fun!) ideas, but the one they went with was an excellent choice!
In "Trials and Tribble-ations" the crew gets sent back in time to the Tribble episode from the original series. They did a great job at blending in the new scenes with out compromising the integrity of the original story. It was a lot of fun to see the cast of DS9 running around in uniforms from the original series!
There are many more things I could talk about from this season, but it would make this a really long post! By the end of the season many things have changed. We learn that Bashir is genetically altered, Odo regains his changeling form, and the battle with the Dominion officially starts!