Nutshell: Not bad, but the one-joke high-concept premise doesn't have enough momentum to remain fresh and wears thin by the end.
When Quark obtains a new ship as a gift from his cousin Gala, he takes the opportunity for a test cruise by transporting his nephew Nog to Earth for his entrance into Starfleet Academy. Rom tags along to see his son off. However, a freak accident sends their ship back in time to the year 1947 where they crash land on earth and are captured by the U.S. military. It happens, no less, in a place called Roswell.
"Little Green Men" has all the indications of a story bought on a single-sentence pitch. I can almost hear two anxious writers coming into Berman's office and saying "I got it! How about we send the three Ferengi back into Earth's past and write them into history. It will be hilarious!" Indeed, this story is a brilliant 20-word concept for an episode. Unfortunately, that's about all it is. There just isn't enough material here to contribute a truly solid hour of DS9. The plot is unavoidably paper-thin and the outcome is pre-defined from square one. There just isn't anywhere to go.
While Behr and Wolfe deliver the comic one-liners with reasonable pace and effectiveness, there's only so much they can do, and there's just not enough momentum here to make up for the obvious lack of relevance the episode has to the series. On the other hand, even if the episode isn't really exciting, it is entertaining enough to chew through an hour. Armin Shimerman, Max Grodenchik and Aron Eisenberg all deliver adequate portrayals of Quark, Rom, and Nog respectively. Though their actions are a tad on the predictable side, they do provide a far more amiable presence than in last season's annoying Ferengi outings, "Family Business" and "Prophet Motive."
There are a number of shining moments, such as the parody on technobabble early in the episode when Rom explains a convoluted way to save the ship from accelerating out of control. I also like the way Nog tells the military officers exactly what they want to hear—that the Ferengi are aliens preparing a massive invasion of Earth. (It's funny how back in the '40s the only possible explanation for why aliens would visit Earth was because they wanted to conquer us. In the '90s, now they just want to con us out of a quick buck). Best of all is Nog's line to Quark, "Have you heard of the Bell Riots?" and his amazement to how much Gabriel Bell looks like Captain Sisko. That goes down as one of the best inside jokes of the series.
The plot is pretty much by-the-numbers. Odo turns up to keep Quark in check (which makes me wonder which is more important: Quark's mischievous plans or the security of DS9). There are also, of course, a couple of sympathetic scientists that help the Ferengi escape the military's clutches. However, the extraneous dialogue between these two scientists—who are engaged to be married, no less—is completely irrelevant and unnecessary.
Other than that, there isn't much to say about "Little Green Men." There's nothing inherently bad about it. It will hold your attention and keep you amused, but that's about all. Just an hour of fluff.