The setup is okay. You are told that after the 17th Apollo mission, the program was scrapped. However, there was one final mission that you didn't know about. This 'found footage' was the assembled footage from that mission. They even try to pass this off as real by giving you a fake website this footage was uploaded to (I already tried looking up the site, but can't find it).
However, if you recognize an actor in the first scene of a movie, the whole 'found footage' aspect is ruined. Not that I think anyone would believe this was a real event. The person I recognized was Warren Christie who's currently on SyFy's Alphas, which I would recommend you watch instead of Apollo 18.
Anyway, they are on the Moon for day and weird stuff starts to happen. They hear things. Stuff seems to have moved around outside. Junk like that. None of it is all that interesting and it just drags along making you wait to find out whatever it is.
There are a few moments that might scare you, but it's all jump scares. Apollo 18 never really succeeds at being creepy. It just succeeds of being boring. Even when you get to the big reveal towards the end, it is totally unsatisfying and actually quite lame.
This movie was directed by Gonzalo Lopez-Gallego, who has only directed foreign films up to this point, which is interesting because this movie had a kind of a foreign film to me, even though it's based on US astronauts.
I don't recommend seeing Apollo 18. This might be better to watch at home if you watched this with good surround sound with the lights off, as I think the sound effects might come off better in a smaller room. Save it for rental or streaming though. Even that's stretching it.
I really wish I would have hung around and sneaked into another movie, so I could have felt I got my money's worth today.