I've just rewatched "Emissary" - starting my rewatch of DS9 (I don't think I'll be watching all the episodes, though), and you are right, even though he appears for a total of a couple of minutes, Alaimo is perfect from the word go.
Many of the other actors are obviously not confortable in their roles, which is something I've noticed before. I remember I wasn't too taken with the acting in DS9 when I first watched the pilot. Overall, the characters were obviously still being established, so they come off as a little overstated at times - Bashir's naivete, Kira's anger (people who talk about Kira's "constant anger" must have based their opinion of her only on the pilot). But I also have to say that I found Brooks' acting better this time - he really bugged me before, I think it was because I needed to get used to his theatrical line delivery. Still, he had some good and some very shaky moments (like the scene with Jennifer on the beach) and sharing scenes with such a good actor as Patrick Stewart didn't help. Quark is one of the characters who work really well from the start - Shimerman's laugh after being told he was a community leader is perfectly delivered.
Overall, I found the episode much better than I remembered it, and definitely makes the best Trek pilot ever, by a mile. It is well-paced, presents a fascinating SF concepts with the Prophets/wormhole lifeforms (the scenes with Sisko explaining linear time to them are the highlight of the episode), and despite some shaky acting (or really bad acting - Gul Jasad was awful, thank the Prophets for this Cardassian not returning!), the characters are well established from the start. It is interesting to watch the pilot after having seen the entire series and knowing how they all end up. Which, I guess, it is an experience similar to the Prophets' non-linear existence. Sisko is showing right from the start, with the way he deals with Quark, that he is not a goody-two-shows Starfleet character, and that he is able to manipulate, blackmail and calmly strong-arm people in order to get the job done. Kira's bluff reminded me of her bluff against the Romulans at the start of season 7, and with it, her character was also firmly estabished.
Is it just me, or was Odo's makeup a bit different, and not so good - making him look too human? OTOH, we saw more of him shapeshiting in this episode than in entire seasons later in the show.
Marc Alaimo is a great actor.
100% agreed on this. (mind you, I've never seen a Cardassian that wasn't portrayed brilliantly by the actor who played them).
Well I
have... and it was in "Emissary"! The actor who played Gul Jasad was just awful.

It's like a textbook example how
not to play a Cardassian, or any kind of antagonist role.