I’ve said it before and I’ll say it again: there is nothing more disappointing than a film that throws away a perfectly good premise only to find itself subsequently wallowing in mediocrity. Take for evidence the last-gasp-of-summer thriller “Apollo 18,” which lurched into theaters recently. Its promotional clips and trailers all looked tantalizing; it billed itself as the unholy offspring of “Apollo 13” and “Alien”–In short, it looked awesome.

What could go wrong? Well, as it turns out, just about everything—starting with Spanish director Gonzalo López-Gallego’s decision to frame the entire film in the very tired found-footage meme. That’s right, just like last year’s “The Last Exorcism,”–which was similarly disappointing—and the “Paranormal Activity” films, “Apollo 18” pretends to be found footage; this time official, redacted NASA footage mysteriously recovered and uploaded (we are told via helpful titles) to a website called lunartruth.org.

If you visit the site, you will discover that it contains no content and no links. However, a legend along the bottom of the page states, “This website was forcibly censored. Its contents can be seen in the film. DISCOVER THE TRUTH.” Leaving aside the ridiculousness of the website (isn’t all censoring “forcible”?), the story of the film is pretty straightforward: NASA covered up an 18th Apollo mission in the late 70’s because its three astronauts all died under mysterious circumstances that may have involved aliens, the Russians, or both.

“Apollo 18” feels tired before it even gets off the launch pad; by way of prologue we’re treated to faux-grainy footage of the three astronauts (Warren Christie, Lloyd Owen and Ryan Robbins) enjoying a barbeque, with their accompanying voiceovers explaining the secret new moon mission. The motive for the mission isn’t clear even to them; the Department of Defense is invoked repeatedly, which is supposed to signal to the audience that only very bad things are in store for the astronauts.

After spending no time at all on the actual voyage to the moon, two of the astronauts land on its surface and begin looking around. Soon, they notice strange things like tracks in the dust—some from a dead Russian cosmonaut (Lopez-Gallego rewrites history here with breathtaking nonchalance) and some from…something else. After a lot of build-up and clumsy foreshadowing, the astronauts are finally exposed to the aliens, which are apparently some sort of shapeshifting hybrid that’s part spider and part rock. By the time the little monsters finally show up, you’re wishing they hadn’t bided their time.

Things go downhill from there, and you already know how it ends. What’s most disappointing is that the film wastes what was clearly a carefully constructed set and a respectable budget on nothing more than lots of purposely overexposed film and a few “gotchas.” I spent most of the running time willing “Apollo 18” to magically transform, like the spidery aliens, into something more like “Moon,” a film which balanced action and atmosphere perfectly to genuinely creepy effect. In different hands, this could have been a fantastic summer movie; what doomed it to failure were the silliness of the found-footage premise, the laughability of the aliens, and the lack of any sort of character depth or development for the audience to latch onto. Retrospectively, this film made me appreciate “Alien” all the more for taking none of these elements for granted.

“Apollo 18” is currently in wide release.