So uhm, I've given this a go recently and...
well, I think it's pretty good for what it is. Most of the eroges translated to English so far are sex romps where by the end of the game you've managed to cover almost every fetish out there and ejaculated ocean's worth on the ladies, but School Days is surprisingly tasteful in that regard: there's not that many sex scenes and the few that are...are well, normal.
It's more of an interactive anime than a novel (a very budget anime though) and writing isn't that sharp, but really, show me an eroge visual novel (or a non-erotic high school romance VN)that rises above your average young adult novel in the writing department? Of course one can not really go all Shakespeare in a story about teenage romance, but this is definitely an aspect of visual novels that is generally unconvincing. School Days is not that great in this regard either, but it's not bad either.
The game centers mainly around two girls and there's not much choice with any of the others, so it's not really a dating sim per se. Instead, you're pretty much forced to have something with one of the girls either way, even if you have set your eyes on somebody else. I think those who haven't seen the anime don't feel so restricted since they haven't been exposed to some f*cked up sh*t that would make them run away from a particular character.
Anyway, as I said, there's two characters, but one of them is an insane nutjob and the other is a really down to earth girl, judging from a few different endings and the anime. Actually, the latter is one of the more likeable anime girl characters I've seen, and considering the average female in the medium that's a huge frickin' compliment.
Basically an interactive budget anime with choices to be made in certain sections featuring pretty tasteful sex scenes with relationships that can be either turn out pretty sweet if a bit tense at points or concluding in somebody meeting a violent end.