We all like the Dominion storyline (well, most
of us do
). It changed the game for DS9, and also revitalised the Star Trek universe in a new direction. I certainly don't think it was a bad
However, I was just reading a bit of 'The Making Of Deep Space Nine' over the weekend, and something struck me: in the original pitch, one of the things that was underlined as being important about the wormhole is that the Gamma Quadrant is rich in potential aliens we haven't met before in Star Trek, and the frisson of danger with DS9 being next to the wormhole exists because something new could come through at any moment for our heroes to deal with. There was some feeling of this in seasons one and two, with for example the Tosk alien in "Captive Pursuit", the games aliens in "Move Along Home", the refugees in "Sanctuary", etc. It differed only from TNG (and VOY) in that the aliens would unexpectedly come to the station, instead of our people going and finding the aliens, though they did their fair share of that as well in the beginning. But the big thing was, the aliens were (like VOY, in theory) all new ones. The writers were only being held back by their own imaginations.
Now, while the introduction of the Jem'Hadar, the Founders, and the Vorta and didn't change that overnight, it did seem to me that later seasons basically made this kind of 'new alien races' aspect impossible. The Gamma Quadrant seemed to be defined purely by the fact that the Dominion are there; and rarely, if ever, was there anybody else.
The types of stories that DS9 told had evolved... but did the writers, arguably, dramatically limit themselves by 'closing off', so to speak, the Gamma Quadrant to just being "that place where the Dominion are from"?