Pues dentro de lo que cabe está bastante bien. Es un juego de puzzles entretenido que cuenta con 20 niveles.
Los niveles del 18-20 parecen imposibles pero se pueden pasar con ingenio debido a que la estructura de los niveles sí está muy bien construida.
El juego se basa en destruir bichos(que al final resultan ser Aliens) de 3 colores distintos(en este caso por la gameboy solo es blanco, negro y un tercero con manchas de ambos colores). Los eliminas mediante las pastillas que lanza Mario en la pantalla, tú misión es acomodar las pastillas para que queden 4 de cada color, esto se puede conseguir tanto vertical como horizontalmente.
No lo consideraría mejor que tetris, siento que Tetris es perfecto y no puede ser superado, pero está bastante bien y la música está buena.
-Juego completado en una Nintendo Switch

A good alternative to the NES version. I have the same issues with its difficulty curve as the console version: after a certain point, the game will just up and decide to screw over the player for the hell of it. See my notes here for more info. But as a whole product, you can get a pretty equivalent experience, which is commendable for a cross-plat of this era.

The graphics taking a hit is to be expected - the Viruses aren't really cute in that gobliny sort of way like they were on NES - but I'm surprised to report that the music is a little stronger. Weirdly, it's this game's version of "Fever" that adds the descending melodic scale that bridges loops - striking in its absence from the original. "Chill" is about on-par with its NES version, which is commendable since "Chill" is such a complex song for this sound-chip. Naturally it's not as satisfying to watch the Viruses groove out, but otherwise, you're not really missing anything.

I guess the Cutscene Viruses are underwater rather than in a tree, and there are fewer cutscenes, but when that's the only thing really holding back the NES experience on handheld, you have in your hand a pretty good port. Of a game I don't love, perhaps, but hey.

(Completed via Nintendo Switch Online)

Dr. Mario for Game Boy is an impressive port of the NES original, successfully translating a pretty fun puzzle game to an on the go experience being practically a 1:1 identical with the original. The only real difference here is the lack of colour as it had been released for Game Boy and not the later Game Boy Colour - the viruses and pills are now all black and white. This does lose a slight bit of life, but doesn't affect the game's playability. The music sounds just as good as the NES version, with no real noticeable downgrade.

To "complete" the game, like its NES counterpart, you have to beat Levels 1 - 20 on High difficulty - where you'll get a cutscene per 5 levels. After Level 20, the cutscenes stop. The cutscenes in the console version are much better, in my opinion, as there's more going on - they're not worth playing this version to view. Additionally, after Level 20 the game starts to become extremely hard, to the point it almost seems impossible to continue, so while you can go further than Level 20 to increase scores, it was clearly intended as the "end goal". I found it hard to get to Level 20 even with the save states and rewind of NSO, it makes me wonder how you'd ever get to this point on original hardware. I played through the game to Level 20 on High mode, but foregoed Low and Medium as you only get one cutscene in these difficulties and it isn't much different from the High cutscenes.

Dr. Mario was a very impressive port for its time, but today, it's just not worth playing over the NES version or any other iteration of Dr. Mario. For this reason, while you'll have fun with it, I've decided to give it a fair middle point of three stars. It's especially baffling that Nintendo had rushed to put this one on the Switch Online service before other, more important Mario games, such as Super Mario Land and Wario Land 1 & 2, as it's the same exact experience as the NES version available on the service long before this one.