This is actually a really interesting manga, and I haven't seen anything like it before or since. I picked it up thinking that it was a hentai, but in actuality, it's an informative, almost textbook type of manga about sex that just happens to include a storyline about two people who are experiencing sex for the first time. Their friends, who have all had sex before, frequently provide their own perspectives, showing that different people experience sex in different ways. I wouldn't exactly use this as a sex-ed guide for a younger reader as some of the characters are very crass, but for an adult reader who is curious, it would be a good read. I thought I was decently versed when it comes to sex and sexuality but I learned a few new things, too!
My one complaint with this manga is a complaint that I have in general: why is it that you can flash all the boobs you want, but heaven forbid there be a penis that isn't fuzzed out, or conveniently covered by a dialogue bubble or a carefully positioned leg or bedsheet? If you're going to be informative about sex, be informative about all of it, please.
Overall, the story is kinda cheesy, but it works really well to introduce a wealth of information about human sexuality.