What made the NES great was what others have already mentioned: by 1985 chip technology was at a point where you could do hardware tiling and RAM was cheap enough that you could do nice color lookup tables. Also the NES came out during a video game crash, so competitors were holding back on making new consoles (their latest consoles were a few years earlier).
Also the ability to do simple stored audio wave patterns and not just sine waves and white noise probably mattered a lot.
Another little detail is the controller layout. Nintendo was the first to figure out that "shitty rubber joystick" wasn't a selling point, and a simple d-pad was infinitely preferable for real games.
...which sold eye-poppingly to a mass audience, while the DS and 3DS sold a ton to a more core gaming audience, and the two have merged in really neat ways with the Switch. (I am very much a "core gamer", I'm playing Triangle Strategy right now, but Ring Fit Adventure also owns.)
Also the ability to do simple stored audio wave patterns and not just sine waves and white noise probably mattered a lot.
Another little detail is the controller layout. Nintendo was the first to figure out that "shitty rubber joystick" wasn't a selling point, and a simple d-pad was infinitely preferable for real games.