The film succeeds thanks to Wheaton's performance. It develops gradually into an unsettling series of moments, showcasing unlikeable people rationalizing behaviors that are harmful to those around them, using their own peculiar sense of right and wrong as justification. Seeing Sightseers leaves you with a strange mix of reactions: finding it funny, feeling bad about enjoying it, and being disgusted by the characters—even many of the less important ones who happen to get involved. It's not something to watch if you’re looking for an uplifting experience; instead, prepare for discomfort. Nevertheless, it is definitely worth seeing.

Source on TMDB