The only reason why this game gets so much attention is simply because it's a Mario game. We are all well aware of how bad the graphics of 1980's games used to be. So it will not be right to compare this game by the ones made now. However, for a correct comparison, we should judge it by its features from that time.
To begin with, let's talk about the colour palette. It has a black background in which the other coloured characters appear. This is meant to simulate the darkness present inside a sewer. The Koopas and other enemies come in from both the sides of the pipe. They have done an excellent job with the ambience. But it could have been better if they occasionally showed a few drops of water spilling out of the pipes to show that the pipes were actually running, otherwise it doesn't make sense for so many enemies to just walk in out of nowhere. Also if the enemies are able to go in through the bottom pipes and come out of the top, what stops the other way round from happening? There is no explanation to it.
Then let's talk about the sound. Every time a crab comes out of the pipes, it makes a sound that's more suited to a beach view. Such a sound doesn't suit a gutter. There are just a handful sound effects, the most (read only) memorable being the one played when a level begins. The sounds used in the game suit more to an open world game of that era, such as River City Ransom or ET (if it was good).
Then the levels. Oh my God, this is the one place where this game fails big time. It's the same level repeated over and over again. Don't come up with an excuse of "limited memory at that time" because Pacman also had different levels even though it came one year before. In Mario games itself, Donkey Kong had different level designs every as the game progressed. The level designer of this game had taken a very lazy effort.
This is by far my most hated Mario game. Even if I was in the 80s I would prefer playing some other game like Super Mario Bros, which came just 2 years after this. Nostalgia doesn't bother me in the least because I played this game just to have tried all popular Mario titles.
