In short, School Days is an anime that will show you what could happen if you cheat, so you dont have to find it out yourself. Watching this will probably redeem you from any cheating you ever done. If you haven't and are not planning to do so, do not bother watching, unless you plan to watch this with your girlfriend/boyfriend to harden the relationship. It definitely will.
This piece is not too much about the enjoyment, but about the moral. And the moral of this story is : Do not cheat. Ever.