The film centers around three awkward boys in their first year of high school, who stay at a youth hostel in the Oki Islands having heard that people who stay in youth hostels are the types to be really open about free sex. One of the boys, the real chief protagonist, Jun, plays guitar and writes his own original songs.
His songs and the other 70s rock songs played in the film are its saving grace. Not that the plot or the characters are all that bad, but the music is really the part that puts you in a good mood and makes you smile and relax and not mind so much that the plot and the characters are really pretty undramatic and unexciting.
Personally, I'm not a big fan of the 70s as an era to look to for nostalgia. I guess it works for the music, and for those people who were actually in high school in the 70s and who would therefore associate it with nostalgic feelings of their own... But for me, it just seems an era of atrocious fashion sense and gritty, rundown everything. Had the movie been set in the 60s, like a number of films, including Always Sanchome, are, then there could be a real feeling of Showa nostalgia, for simpler times, the good old days, a rustic sort of feeling the Japanese equivalent of what we Americans associate with... "the Greatest Generation" is what I think it's called. ... But the 70s just don't do it for me.
I don't want to get too much into plot spoilers, but let me just say this. If you're looking for a movie that creates drama and excitement using standard, stereotypical Hollywood tropes, this isn't it. If you're looking for a movie that creates drama and excitement by deviating from those tropes in interesting, surprising, or innovative ways, this isn't it.
But if you're looking for a movie, largely lacking in drama or excitement, which is just relaxing, with a good mood happy sort of feeling, good music, and something of the innocence, naiveté and awkwardness of being in high school, and especially if you enjoy the aesthetics and fashion of the 70s, this is certainly a fine choice for that.