Personally, I think it's a good one. Most (If not all) of the story will get serious after the common route, and that's a good aspect IMO after all the 'fun' times during the common route. Depressing? In some way, yes. In my view, however, Kotori's route is somewhat the most "depressing" for me, and not to mention one of the heroine's routes which I won't mention in order not to ruin your experience. Still, I don't think the other routes are as depressing as Kotori's and a certain someone's. Though I wouldn't call those exactly depressing...Maybe bittersweet? Overall, I think Rewrite's an amazing read.