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 ie 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. Plus Keating calls out Charlie when he goes too far and pulls a prank. Plus, he did first have the students read the text and gave a brief, impassioned explanation for why he disapproved of it. It was more an act of rebellion than true censorship and the students could always make up their own minds about it.
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. About the worst thing he does is fire Mr. Keating following the scandal caused by Neil killing himself — and even then, it's an act of damage control, not motivated by spite or cruelty.
Nolan 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 to be "excellent", and disciplines Charlie for his silly prank by paddling him. His portrayal as the bad guy seems quite justified.
Harsher in Hindsight: 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 could 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.
Jerkass Has a Point: Keating's antics don't go over well with the school administration and teachers. He has at least two conversations about this during the course of the film. While the audience is set up to believe their adherence to tradition and conformity are a bad thing, both conversations drive the point home. "Free thinkers at seventeen? Teach them to learn and the rest will follow." A prep school education is designed to send the young men on to college, and trying to be an artist will only end in disappointment.
Launcher of a Thousand Ships: Charlie is paired with nearly everyone in fanfiction, mostly under the logic that he probably wouldn't object.
Memetic Mutation: The "carpe diem" speech got a lot of play on Tumblr in the wake of Robin Williams' death.