The music in this game is by Hirokazu Tanaka who also composed the music for Duck Hunt, Earthbound, Metroid, and fittingly, Tetris. The music in this game is fairly straight forward in use: there's music for the title screen and selection screen, and, like Tetris, there's a choice of music during the gameplay. Otherwise, there's music when you win or lose the round or the hardest level of gameplay. The ending is different depending on the difficultly, and that's reflected in the music as well. If you beat the game on the highest level and speed, you hear a slightly different level clear than you would on a lower speed. Also fascinating that the highest level clear music and the end game music are the same.
Something I was aware of when I was younger but had forgotten was that the "fever" music is quite a bit shorter than the "chill" music. As I note below, the Chill music is nearly double in length compared with the Fever music. Wonder why that choice was made? Also thinking about the comparison of description between "fever" versus "chill." One is clearly more upbeat than the other. (Fever is 150 beats per minute, while Chill is a more moderate 128 bpm.) Recent studies have shown that listening to music of too high intensity negatively impacts gaming performance. I don't think Fever approaches that level, but cool to think about the ability to chose the background music. I definitely remember thinking about and deliberately choosing which music would help me to focus better, so I feel certain that the connection between gameplay, focus, and accuracy was something I intuited as a young person.
Here's a long play from cubex55 (love this person!) so that you can see the ending screen if you never did. I certainly never saw the UFO as a kid.
Dr. Mario has just a little less than 8 minutes of music. This is way less than many other NES games released as late as 1990. Perhaps this was because of the simultaneous release for the Game Boy? Perhaps the design play was simply to keep the same music but to adjust for the nuances of each systems technical limitations. The simplicity of gameplay definitely seems to be indicative of a Game Boy game, as is the short amount of music.
Here are my detailed notes as you're interested. This music has a distinctly pop feel. Reminds me of the 60s. These notes were compiled using this soundtrack.
-Title Screen: 64 sec. A major. Intro A A' B A''. Sounds like a 60s song, modulates to IV for the B section. Heart and Soul sound?
-Mode Select: 19.5 sec. F# major. A B(4).
-Fever: 67 sec. G major--> C major. Intro (2) A A' (in C) B A' (4, 2nd half) C (break) (12). This was the music I listened to most often when I played. Reminds me a bit of Super Mario 3 Hammer Bros battle theme, which is also in C! Boogie Woogie?
-Fever Clear: 22 sec. E major.
-Chill: 1:59. A minor (major moments). Intro(4) A B C(4) D E F (12) G(4) H Intro doesn't repeat with loop. Almost twice as long as "Fever." Through composed, but really mainly a set of variations over a bass.
-Chill Clear: 21 sec. F major--> A minor. Starts with same fanfare as Fever Clear.
-Game Over: 23.5 sec. Chromatic.
-Game Over Vs: 53 sec. E major. Fanfare- A B A' B'. A'/B' are melodic variations over the same bass. Quite a bit longer and more developed than the regular game over music. Were the designers giving more time for you to gloat?
-Level 20 Clear (low): 17 sec. B major. Intro- A. Intro doesn't repeat.
-Level 20 Clear (UFO): 59.5 sec. G major. Intro A(4) B A(4) B' Irregular meter. 4's of A and B add a beat. Same musical theme of the low clear.
-Ending: Same music as Level 20 Clear UFO