This episode truly did look like it was going to be pretty weak - oh great, Sisko, Jake, Quark and Nog go off to some planet, I wonder what wacky adventures will ensue? But then...
The series had been teasing the viewer about the Dominion for a while now, but to have them suddenly show up in such an explosive way was really effective. They really pulled off an "everything's different now" moment and it was a defining point in the evolution of the show.