The Cuphead game is clearly based on 1930s animation. That decade may not be as defined and realistic as 40s animation, but it was still highly principled work, and movement was often more realistic than the CalArts TV shows you get today. But the point wasn't to make movement as realistic as possible then. The goal was to animate as smooth, lively, expressive, and constantly as they could achieve. That's why 30s animation tended to incorporate heavily surreal, illogical, and fantastical elements. It's something that looked nice, but you could never achieve through film. That was the whole appeal. If you could get realistic movement while doing that, (which a lot of late 30s animation achieves), that's just a bonus.
The Cuphead game's animation looks to be primarily based on the work of Grim Natwick. They even named a character in the game after him. It's understand why they didn't try to achieve Grim's style and level of quality in this economy, it would surely take a lot more skill and manpower than the style they went with, and therefore be a lot more expensive. But if they could do it, it would have made for an amazing series.
Hopefully it still turns out to be good. I'm not sure about the animation or the dialogue, but the designs and backgrounds look fine.
Grim Natwick shorts for reference:
https://youtu.be/FSm07stzHZQhttps://youtu.be/BQhO3rSP5ukhttps://youtu.be/1rixfK0Fuvwhttps://youtu.be/M8akUR_9khAhttps://youtu.be/QudEjNQTwXY 
