How well does this episode work as an introduction for the Dominion? I honestly can't say because I missed it when it first aired and by the time I saw it I already knew a whole bunch about the Dominion.
I did watch it first run and it kind of had an "alien of the week" feel to it, but I'd just come off of watching TNG for years where every alien was "of the week." Trek hadn't done any kind of long term arc, nothing more than a two-parter and since this was the season finale, that's what I was expecting out of it.
This was the first episode of DS9 that I'd ever seen. TNG was ending and I needed a Trek fix. My mom had been watching DS9 from the begining, but I thought the whole "no ship, no Captain" thing was stupid. After watching this episode I was hooked (and in the upcoming seasons DS9 would get both a ship and a Captain).