The gameplay is classic run-and-gun with an emphasis on boss battles.
Here are some character sketches. The game uses traditional hand-drawn and hand-inked cel animation animation and painted watercolor backgrounds. A lot of the animation is on cycles.
The bosses have rolling eyes and pop-out heads. Effects animation includes little puffs of smoke when Cuphead hits the ground and star-flash FX on shots and impacts.
The period style is hard to nail down to just one era. The animation style owes a lot to Silly Symphonies like Hell's Bells (animated by Ub Iwerks) and the madcap mania of the Fleischer Studios of the 1930s. But the game also has a 1920s vibe because of the silent-picture title cards (complete with digital chromatic aberrations and "projectionist" focus pulls). The jazz music track has a bebop sound that places it more into the '50s.