Kicking off Star Trek with a horror episode, "The Man Trap" (which is really a misnomer since it also proves to be a woman trap) is more boring than frightening with its languid pacing and emphasis of guest stars over the regulars. By all accounts, writer George Johnson really wanted Star Trek to succeed and worked hard on the script, and he does deserve credit for developing one of the franchise's key plots: the crew beams down to a planet, discovers a threat and tries to deal with it. We even get our first televised "extra" deaths on the planet, though they don't know yet they're supposed to be wearing red shirts! But the construction of the plot is clunky, with Johnson seemingly unable to make up his mind as to exactly what kind of creature this is. Early scenes emphasize its ability to appear differently to different people, with Kirk even including the notion in his log. (How he knows this is a mystery, especially since Kirk and McCoy see essentially the same woman and the other crewman involved has no chance to describe his vision). Later, the creature continues to shape-shift, but its appearance seems be consistent to everyone. It's not technically an inconsistency; there's nothing to say the creature can't assume the same shape in everyone's eyes. But why spend so much time early in the go showing an ability that will be dropped and not factor into the plot?
Guest stars Alfred Ryder and Jeanne Bal do the script no favors. If ever an episode needed a sexy actress to help us through the dreariness and lack of action, this one is it; as is, Ryder and Bal and capable but nothing special.
All in all, this is Star Trek still trying to figure out what it is and stumbling a bit. You certainly won't see this one in a marathon of best episodes, but it also won't be laughed about as one of the show's worst episodes. It's a bit of an odd choice to be the first piece of Star Trek to make the air.
Remastered Edition: Since the original version of "The Man Trap" includes only basic special effects, and, with few bridge scenes, doesn't even include anything of interest on the view screen, the remastered edition's only notable changes are the Enterprise flybys coming out of commercial break. Appropriately, the new version keeps the same (standard) angles and (like the original) doesn't let the flybys call attention to themselves - with the exception of one artistic shot from above the ship late in the episode.