This series of 4 horrors are truly the best in asia. Simple, logical and terrifying. J-horrors are sometimes too loose, and some directors can go too far away from a good story. Korean movies are usually on the slow hit compared with other Asian films. Yet these 4 movies keep rather good paces.
The "dark forrest" is the slower among the 4, and it's quite confusing the first part. Although it's a good trick, it's rather small and has been kept too long. "Hidden floor" is not my favorite either, but the acting of both mother and girl are quite natural and convincing.
This one, "Feb the 29th", is fairly scary. Perhaps because I personally know similar places as what's in the movie. It's a good tale, a gripping urban legend, while the alternative/scientific explanations alleviate the intensity of horror. Borrowed some Ju-on gimmicks, so as "hidden floor", but it seems to be universal after the success of Ju-on :)