What's special about DS9?
I could into a VERY long and detailed post... or essay... on why I think DS9 is special and the best series of the feanchise. But a lot of my feelings can be summed up in a couple sentences.
From the start, it felt like a real, lived in place, and the characters were the most real characters. Every... single... one.
Having an excellent cast with a LOT of theater background between them, sets that were beautifully designed, and a writing staff that played to the actors' strengths were among other secondary reasons why DS9 is and will always be my favorite STAR TREK series.
I think the better question is, "What is NOT special about DEEP SPACE NINE?"
The answer... is nothing. It was an almost magical feat that everything came together like it did. It's going to be near impossible to recapture that level of magic again.