Which potentially antagonistic race would you like to have seen pitted more against Starfleet? For me, it would be the Breen.
Tholians. They are the most exotic alien race and, because of budget reasons, only dealt with two times. And I don't count the second time because I don't like Enterprise.
Agree on the Orions. Should have been seen more during "Enterprise". Should have been seen during TNG, maybe as the occasional green Sterfleeter, implying that some of them, at least, were not nefarious. We heard a lot during DS9 about the "Orion Syndicate", but when we finally see them, they're a mixed bag of humans and aliens.
The Orions did quite well in Journey to Babel (considering they were up against the Hero ship), they put one of their people in the Andorian Ambassador's staff, and they attacked and damaged a starship. Against a different Captain it might have worked. It would be interesting to see our crew against a opponent who was a business interest, or a criminal organization. Not just another anti-Federation star empire (been there, done that).
Whomever it was upon whom Balok based his false appearance. I like to imagine it an ancient enemy of the First Federation.
Oh, and the First Federation. If it were up to me, Peter Dinklage would play a Diplomat in the next movie.
Tribbles. Sure they look cute and unaggressive, but they'll bury other races under the weight of their quick breeding population.
Agreed. I can see the Great Crystalline Entity as Tholian-related--Narada looked more Vorlon to me BTW.
The Sheliaks, I agree. From what is explained in that episode, they signed a treaty with the Federation, but they seem to be mighty adversaries with really powerful technologies, they were capable of transporting Picard and Troi out of the Enterprise without interference, and they appeared to have deadly weapons that could have make the human colony disappear off the face of the planet.. Their only weakness (or strength) their lawyer-oriented culture: Picard only needed an obscure footnote in a text to make them comply.
The Sheliak also perhaps did not take war with the Federation quite as lightly as their initial posturing suggested. I loved the Sheliak, not a little for their kitsch value; the Sheliak envoy Picard speaks to reminded me of the B-grade, low-budget aesthetic of TOS, looking like something the props guys bashed together using a sleeping bag, an accordion and a lava lamp. Beyond that, however bad the effects were, one always has to applaud the effort taken to include non-humanoid aliens.