The only Star Trek series not taking place on a Starship and instead a spacestation, Its my personal favorite of the five.
Deep Space Nine is alot darker then its predecesors focusing alot on war against the Dominion from the Gamma quadrant, And the tension between federation and cardassian borders, More so since Deep Space Nine works as a guard to the first stable wyrmhole wich makes it a target for alot of various factions.
One thing that did this show better was Miles O'brien who played a support roll in The Next Generation got a permanent spot on this show, And alot of episodes has him in the center, And it really worked well to have a familiar face around, Worf joins the team in later seasons aswell.
While watching this show I cried, Laughted, Felt happy and sad, Its definetly in my Top 3 shows ever, So if you want to give Star Trek a try, This is a good choice. (Ofcourse I prefer to watch all of them in order for the timeline).