New York New York (1977)

Plot:  A Saxophonist and Big-Band Singer have a tumultuous relationship while trying to make it big.
Stars: Liza Minnelli, Robert De Niro
Alternate Title:  Raging Bull - The Musical
Best Negative Comment: Occasionally repellent but mostly tedious and trite... Liza Minnelli, difficult to like at best, comes out looking like a giant rodent en route to a costume ball..

An Interesting Failure
Scorsese's DVD commentary tells you - unintentionally - why New York, New York was a box-office bust and currently has mediocre 6.7 IMDB rating. Martin talks endlessly about the look of the film, the set design, and his desire to do a revisionist musical.  What's rarely discussed?  The characters, dialogue or music! But that's what people want in a musical - good story, good songs, and engaging characters. And a few laughs never hurt.

Instead we get  the most unlikable Musical Leading man - ever
For the first  2 hours  the movie is dominated by De Niro, playing "Jimmy" -  a hot-headed, obnoxious, unstable motor-mouth. He's a walking poster-boy for Sexual harassment and childish egotism.  His most "endearing" scene shows him posing as a disabled vet - to get out of paying a hotel bill.  And he has 60% of the dialogue.

Liza  and the Puzzling Love Affair
Meanwhile, Minnelli is given a passive character - who just reacts to De Niro. Sometimes she fights back, but mostly she's just looking at De Niro with her mouth open in a smile or shock.  And what does Liza see in him? It's never made clear. When they break up, you aren't sad - just relieved.   As you'd expect,  Liza and De Niro have zero romantic chemistry.

Supporting Characters? Who needs 'em
Even worse, De Niro and Liza are the whole movie.  They have 90% of the dialogue and every scene is about them. Unlike your typical 40's musical, there is no love triangle, subplot, or "Best Friend".  The three main supporting actors are just cardboard cutouts:  Liza's agent, Liza's backup singer, and the guy who buy's De Niro's band.

The Positives
The set design and direction are great. Scorsese wanted an "old fashioned MGM musical" look and gets it.  He uses back projection, realistic costumes, and the same montages and colorful nightclub signs you'd see in a 40's musical. As for the music, we get an excellent long sequence, some old standards, and New York, New York. You can't blame the failure on Minnelli's singing or even De Niro's acting. Its a script/story that's the problem.

The Horrible Dialogue
Two and half hours long, and not one memorable line. According to Scorsese, most of it was "improvised" which probably accounts for the verbose and repetitive quality of so many conversations. Sample:

Liza -I'm going to back to New York 
De Niro -What do you mean?
Liza - I want the baby to be safe. I need to go back to New York
De Niro -You're going back to New York?
Liza - Yes, I need to go back - for the baby
De Niro - I'll get you a car.
Liza - I don't want a car.

Worst Scene -  De Niro and Minnelli argue with 2 nobodies over a parking space.
Best Music Scenes -  First, the Happy Endings movie within a movie. Second, Liza sings "You brought a new kind of love to me" to win them a new band gig.

Summary:  163 minutes long with 40 minutes of Liza singing and  2 hours of De Niro playing Jake Lamotta with a Saxophone.  Here, quantity doesn't mean quality -  and we needed a better story, better dialogue, and a lot more charm. Sure, it looks great and has a few good musical numbers, but there's too much unlikable drama to slog through.