DS9 - Little Green Men, Our Man Bashir
LGM has aged extremely well despite the latest means to engage time travel as a plot device. Charles Napier is a coup of casting. Odo is deftly written in, not spoiled by his shapeshifting into a cog on the ship console to wink at the audience lamely but doing all that offscreen so we can get the nice reveal of him as a doggie (how did Odo figure out to get the behavior of a guard dog down pat? Never mind, "it just works". Actually, he's observing what other doggies in the vicinity are doing and reminding us he's ideal as the space station officer that always keeps tabs on Quark's slimy antics, this stuff is great!) I don't think DS9 would vanish (per Nog's worry) but changing Earth history would likely lead to no Federation. We all know history would not be changed but the makers knew the format and how to make the ride interesting for the one-off episode. Even with Garland paraphrasing Kirk's opening credits as an in-joke (I'd be more surprised if time travel episodes didn't do that.)
OMB ties in a neat arc strand (terrorism against the Federation) into what becomes a high concept filler episode that's entertaining as all heck and allows the actors to do something different and Avery Books and Alexander Siddig steal the show. Nana Visitor's voice with the accent actually sounds really good too. Great homage to the 1960s spy genre (notably Bond and UNCLE, but there's a moment of even 'Get Smart' in there very subtly as well). Roll with the convoluted premise to get the crew stuck in a Holosuite 3 program with the Safety switch off and there's way too much to enjoy to knock off any big points.