Alternative Character Interpretation: Did Nolan fire Keating after Neil's suicide because he honestly believed he was responsible for it? Or was it an act of damage control to save the school's reputation? Or did he just use the incident as an excuse to get rid of him and his unorthodox teaching methods?
Was Keating an irresponsible teacher for going against the school's values and rules despite the consequences, or was he doing the students a favor by trying to open their minds and broaden their perspectives?
Broken Base: Some viewers feel Keating was an irresponsible teacher, encouraging the students to break the school rules when in so doing it could get them in trouble but would be unlikely to rebound on him and he tried to censor ideas that he didn't agree with, ripping out the book introduction. Others feel that the value of broadening the students' perspective and encouraging them to enter adult life with a different attitude than that endorsed by the school was in the long run worth the short-term risk of being disciplined by the school.
Designated Villain: Principal Nolan has some of this, the movie setting him up as the uber-conformist, stuffy-conservative "Stop Having Fun" Guy opposite Mr. Keating's free-spirited Cool Teacher. While he is a jerk from time to time, most of the time he's just doing his job as principal of the school; the rest of the time, he's espousing beliefs or values that clash with the message of "Carpe Diem", which is hardly his fault. On the other hand, he clearly believes that the authoritarian structure of the school should be maintained, considers the ridiculous essay about drawing graphs to analyze poetry that Keating condemned as "excrement" to be "excellent" and disciplines Charlie for his silly prank by paddling him (though it was deemed much more acceptable in 1950s than it is now).
Mr. Keating breaking down in tears after he discovers that Neil killed himself is a thousand times worse to watch since Robin Williams committed suicide. It also makes Mr. Keating's speeches about "carpe diem" and seizing the day before it's gone heartbreaking.
The film's final scene has Keating's students giving him a touching send-off, showing their appreciation for everything he's taught them. This is now almost impossible to watch without feeling like a send-off for Williams rather than his character. However, it can be considered Heartwarming in Hindsight, since they're showing how much he meant to them.
Ho Yay: Neil and Todd. It's virtual canon, to the point that most of the fanfiction circles on them.