The first time I ever saw this movie was when I was four years old. I remember loving it and everything about it. 13 years later, I am now 17, and decided to watch it about a month ago because I am taking a 1960's class in school. I didn't really know what to expect, since it had been 13 years since I last saw it, but I was completely blown away by it. The actors were amazing, the music was so fun, and I now find myself singing along to every song. Treat Williams is great as Berger, the "leader" of the hippie group, who always gets what he wants, one way or another (except for at the very end, of course). John Savage is actually very convincing as Claude, the Oklahoma draftee who falls in love with Sheila (Beverly D'Angelo). D'Angelo is lovely as the prim and proper rich girl who eventually rebels against her upbringing and joins the hippies. The other hippies are played by Annie Golden, Don Dacus, and Dorsey Wright. Annie Golden is just adorable as Jeannie, the girl who is pregnant but still as cute and innocent as a child. Don Dacus and Dorsey Wright are good as Woof and Hud, the other two members of the group, and Cheryl Barnes, who plays Hud's fiancée, has an amazing voice.
The only problem I have with this movie, however, is that the relationship between Claude and Sheila is not very convincing. They are barely ever shown together, and when they are, they fight (remember the skinny dipping scene?). It seems as though their relationship is very weak, and by the end of the movie we are supposed to believe they are madly in love, only based on the few meetings they had. I also see that many people writing reviews here are upset by the PG rating this movie has. I personally would raise the rating up to a PG-13, only because there is some drug use... but remember in 1979, PG-13 didn't exist. I don't think the nudity is bad at all, it is in no way sexual (in fact, there isn't really any sex at all in this movie), and it is only to show the childlike innocence that the group maintains. In most European countries, nudity isn't regarded as something bad, and I don't see why it is here in the US. Anyways, I give this movie a high rating, and I'm glad it was made back then, because in the insanely "politically correct" world of today, they wouldn't even think of making it, and even if they did, it would be a very "watered down" version, and I'm sure you wouldn't get the full effect.
In conclusion, this is a very underrated film that is definitely worth checking out.