I was given School Days (among many others) to put on my to-watch list by a friend who was trying to get me into anime. It was the second anime I watched and truth be told I really enjoyed it. All I was told is to stick with it until the end.
The characters at the start are all fairly likeable and as the story takes place each character changes and it is for this reason I can understand why a lot of people are turned off by it, but (following my friends advice) I kept watching until the end... thank god I did. I appreciate that a lot of people don't seem to agree with me and it is maybe because I generally like most things I watch and don't really think about flaws; this series does have its flaws but overall I enjoyed it!
