I enjoy watching Thai movies, especially when they have subtitles. I can speak Thai, but for me, watching a movie is supposed to be enjoyable and translating inside my head feels like I have to constantly do math and I would prefer to not do that. Pee Mak is a comedy disguised as a horror movie. Parts of it are a bit gory but for the most part it is meant to make you laugh.
So, I said that this film is not good and that is mainly because it is childish and annoying yet the films is not meant for kids anyway which is evidenced by the amount of swearing (Thais are significantly more conservative in regards to this than in the west.)
The story begins with 5 friends who are soldiers that are involved in wars that were a regular thing during the 19th century in Thailand. After getting discharged or allowed to go home, the first place they go is to Phra Khanong, which is where "Mak" is from so that he can see his wife had a baby while he was away at war. This is where the movie takes on elements of actual folklore and Thai spirituality.
They return to discover that there are rumors that "Nak" (the wife in question, who is married to the main character "Mak") is dead and that she is now a ghost - yet it doesn't appear that way to Mak and his friends. Things change as the story goes along.
The reason why this film is interesting is because there is a huge amount of ghost folklore in Thai culture and Buddhism. I would almost call it childish and irrational. Fully grown adults have been taught when growing up to be exceptionally afraid of spirits and ghosts, and while I know a few westerners who feel this way, they are few and far between.
The adults in this movie are extremely afraid of ghosts and act in a completely crazy manor at just the thought of someone being a ghost or having seen one. This seems over-the-top and slapstick-ish, but I can tell you, there are many Thai people that are genuinely afraid of exactly this. The fact that this movie is based on a somewhat well-known lore of Mae Nak Phra Khanong (a Thai female ghost) is what makes this film particularly edgy for Thai people familiar with the stories.
This movie is the highest grossing Thai movie of all time and this is quite surprising to me because there are some serious Thai films such as Ong Bak and Tom Yum Kung that are far more entertaining (to me) but since I'm not Thai maybe I just can't identify with it very well. I don't think this movie is worth watching from end to end unless you are interested in seeing a glimpse into Thai culture in relation to fear of ghosts. The screaming and whining of the 5 men in the film becomes quite annoying after about 30 minutes.