7. Halfway agreed here.
Otome: I think this one checks out for the most part. Otome's had plenty of time to develop feelings for Makoto because they were good friends during middle school (And speaking as someone that watched the first three episodes just yesterday, Makoto's a perfectly likeable guy at the start), and Makoto reciprocates because she's a hot chick. The only part that breaks suspension of disbelief for me is the timing, the fact that Otome's liked Itou for years but doesn't confess until the most dramatic time possible (ie when he's already stringing along both Sekai and Kotonoha).
Setsuna: I have mixed feelings on this one. Screwing Makoto despite with Sekai is
kind of in-character considering her excuse and rationale, but it's a stretch.
Hikari: I think I read somewhere that in the game Hikari gets with Makoto to take her mind off Taisuke, which is fair enough. It's extremely random in the anime, yes.
Foursome Girls: A lot of people say this is completely unrealistic and over-the-top, but I don't agree, really. Yeah,
most girls wouldn't do anything like this, but there's a lot of people in this world, and some of them are unique and do or say things that few others would. Is it completely impossible for a few depraved girls to go "Hey, let's have a foursome with that guy"? Not really. I have trouble buying into things like the 'condom in hand' ritual because it requires the bulk of the student body at Sakakino Academy to act fucked up, but I don't have a problem with a few
individuals diverging from the norm, particularly individuals with very little previous screentime or characterization. I do think this was put in purely for shock value, and I do think it's silly and disrupts the mood, but I don't think it's as unquestionably ridiculous as most people or that it turns the series into a downright comedy.
8. Hypocritical, maybe, but this dampened your enjoyment of the show? It seemed perfectly realistic and understandable to me. Sekai was Makoto's secret girlfriend for about the same length of time that Kotonoha was his real girlfriend, and unlike Otome (Who was content with being a mistress and nothing but), Sekai thought Makoto cheated with her because he loved her. I really can't blame Sekai for having expectations or demanding some kind of commitment. And, for what it's worth, Sekai discovers she's been cheated on (End of episode 10) shortly after Makoto dumps Kotonoha, so she's not the 'other woman' at that point to any extent.
9. Not sure what the problem is here. Makoto and Sekai fucked like rabbits, babies are a pretty natural result.
10. Makoto wasn't completely oblivious to Kotonoha's pain. He just didn't want to deal with it.
Makoto's a very selfish person, but he's not completely uncaring about the people around him. His
own feelings and his
own sense of personal comfort are his first priority, with the feelings of those around him a secondary priority that becomes increasingly more distant depending upon how much of a burden or obstacle those feelings represent. Makoto's personal philosophy throughout the entire series is "Always look out for number 1 - but if number 1's okay, then you can worry about all those number 2s." He was pretty heartless towards Kotonoha in episode six, didn't so much as raise an eyebrow when she tripped and almost hurt herself, because she was getting in the way of his Sekai fling and regarded her as an annoyance and burden. In episode 11 when Sekai cried into his chest asking why he cheated on her, he shut off his emotions because tending to her feelings would be too much of an inconvenience; he wanted to continue sleeping around and getting some ass.
In situations where being caring does not require also being self-sacrificing, though, Makoto is consistently sympathetic in almost every situation that should inspire sympathy. In episode 7, he glares at Minami for picking on Kotonoha; 10, he's obviously pissed at Setsuna for the psychological warfare she breaks out on Kotonoha. The end of episode 11 is one such situation, and seems perfectly consistent with someone who's caring whenever being caring isn't disconveniencing. Makoto does have a heart, it's just that sometimes it's overriden by his dick (And his general unconfrontational personality; it should have been obvious from episode 1, his aversion to actually speaking with Kotonoha even after Sekai arranged them a date, that his attitude towards dealing with problems is 'Don't').
So yeah, I believe Makoto's response to the broken Kotonoha was both very genuine (I don't agree with those who think he just apologized to Kotonoha because she was the one piece of ass he could still have) and still perfectly in-character.
11. Again, I somewhat agree (Though more than just halfway this time). The ending was just the writers wanting School Days to go out with a bang and give the fans what they wanted. I do have to give the ending partial credit, though. Although I don't believe Sekai had been pushed to the point where she legitimately might murder someone (Whatever flaws she might have, Sekai was a perfectly balanced girl for pretty much the entire series, and during episode 11 was just severely depressed, which isn't really a prelude to 'homicidal rage'; I do think the events of episode 12, particularly the frenching between Makoto and Katsura, would have
severely messed her up, but not to the point of murder), it's at least built up to an extent that it's not gratingly random and over the top (ie the School Days manga); it's more just a 'Yeah, that probably wouldn't happen.'
As for the severed head thing, I think it's actually perfectly believable. Sekai and Kotonoha being driven to the point of murder is one thing, but cutting off a corpse's head... well, decapitating a dead person isn't such a big deal in comparison considering that the person's already dead anyway, you're not really causing any sort of loss or harm to someone. All that requires is a strong stomach, morals don't really come into play anywhere here. I think it's the most believable element of an over-the-top ending.
School Days isn't perfect, but I've personally always found its pacing and plotting very meticulous and commendable, sans the ending which is pretty much completely divorced from reality (Though I still like it as much as anyone else).