2014 update: Alfonso Cuarón, the director of Y Tu Mamá También, finally has been recognized for the genius he is, winning an academy award for best director for his movie Gravity.
I will go to some effort to make this review as spoiler-free as possible.
The movie Y Tu Mamá También is one of those rare movies that had the same intensity the second time I saw it as the first time. It is a movie that, at the very first layer, seems to be a shallow movie where we see people act out the typical male sex fantasy: A pair of young men who get to make love to some very beautiful girls. I initially discounted this movie as an expression of the sexual desires of mexicanos living in a world where girls are commonly virgins in their 20s and where the sexual revolution of the 1960s never took hold. I soon realized that this was a misperception.
The raw way in which people's sexuality is expressed in this movie, of course, will be shocking to Americans. The scenes are rather shocking to my Mexican female friends--I do not have a single female Mexican friend who has confessed to liking this movie. This is real sex here; it is even possible that the actors made love during the filming. This movie does not put sex on a pedestal the way a similar American movie would have. We can see that the people are not particularly enjoying the sex. Sex just is in this movie; like the drug usage and the scenes where we see people going to the bathroom, this movie has no qualms about honestly showing these people's lives.
Beyond the shallow layer of the teenager's sexual desires, Y Tu Mamá También has many layers. Just one example: Near the end, one of the characters says "La vida es como la resaca", which is roughly translated as "Life is like the surf". The word resaca, however, has many meanings; it can mean "surf", but it can also mean "serf" in the sense of being at the lowest level of society, in addition to being the word used to describe a hangover. The many meanings of what the character says perfectly fits in with the plot.
The masterfully crafted plot is only fully unraveled at the very end; everything fits together perfectly. This is a story that could really happen; there are no plot holes. This is a movie where I felt I somehow had a magical view of real people's lives; I felt true compassion for the sufferings that the characters were having in this movie.
This movie is in Spanish, but has English subtitles. The web site has a glossary of the crude slang used in this movie; anyone fluent in Spanish but not familiar with Mexico City vernacular should read the glossary before seeing the movie.