From what I gather from Wikipedia, clips on youtube, and various discussions is that the game is still pretty dark and more about taking advantage of the girls and cheating than about romance. Only 3 of the 20 some endings are violent, but some of the others I've heard about still seem kinda cruel or unhappy (like the "Goodbye Sekai" ending)
There's an alternate retelling spinoff, Summer Days, that has the same characters (though it focuses on Setsuna) and is apparently more of a typical light hearted h-romance. No NICE BOAT endings.
Both games are fully voiced and animated, and aren't very interactive (just yes/no/no responses pop up at the bottom at major decision points, although there's apparently some sort of chance factor to events popping up or Makoto's nonresponsiveness to some of your choices that makes playthroughs different). So I'd assume it would be more like watching an anime then playing a game.
I've heard there's a translation project for School Days, but it's stalled... and I've also heard that there was an "official" english demo released on Overflow's web page, but it was just an April Fools joke.