Aaron Noonan’s review published on Letterboxd :
Oh my. That was not what I was expecting at all. This film is so fantastic. It truly is one of those films that, in the hands of another director, could have been an unmitigated disaster. But Scorsese and De Niro just transform it into pure gold.
Rupert Pupkin is an aspiring comedian, who dreams of appearing along side his hero and mentor Jerry Langford (essentially Jerry Lewis playing himself). Over the course of his life though, Rupert's dreams have turned to obsession and desperation, and eventually to stalking. He craves Jerry Lewis' recognition, and will do anything to get it.
Rupert Pupkin's character is so brilliantly realised by De Niro. He's a sad, sort of hapless character that we pity, but he also makes us feel just a little bit uncomfortable, like he could do something threatening at any moment. Not many actors can do that, probably none as well as De Niro and I genuinely feel like this is my favourite performance of his ever.
The script is genius in how it builds up to where it ends up. I would defy anybody to guess where the film is going until at least half way through the film; I'd doubt anybody could. How it plays out is great too. The switching between reality and Pupkin's fantasy happens often, but we're given little to no indication of it by Scorsese. Sometimes we don't know if we're watching Pupkin's imagination, or reality. This is great, because it shows that Pupkin doesn't know either. He's essentially a mad man (albeit a well meaning one), but his lines have become blurred, his imagination has become his reality, and when he arrives at Jerry Langford's house for the weekend he doesn't even realised he imagined the invitation. Genius.
While The King of Comedy is at heart a social commentary on the culture of celebrity, is also a fantastic character study. We learn so much about Pupkin throughout the film, and in such interesting ways. Through his fantasy sequences it's easy to see what makes him who he is - an apology from his high school principal show his unhappy past; his fantasy of marrying Rita live on the show when he's a guest is so utterly bizarre, but really it's just the coming together of unrealised dreams; the scenes when he's at home acting out conversations between himself and Lewis - all of these build up a wonderful character profile of the man. He's a mad man, but it's hard not to love him.
The ending as well is wonderful. I won't go into it as not to spoil it, but the ambiguity of it suited the tone of the film so well.
I really cannot over state how good De Niro was in this. This film was so much more than I expected it to be, and it's definitely as good as Taxi Driver and Raging Bull. Why the devil it doesn't have as good a reputation I will never know.
(Also, as an aside, I realised watching this that Father Ted parodied a scene in this once. Made the film even better, if that were possible.)