That fact that you mentioned getting to level 81 makes me LMAO. Inside thing. I never played this NES version but I own it many times over; E-Reader, Atari 7800, Super Mario Advance 1-4, etc. so I've never needed to try this version. It's easy to find but it never gets old. I can always go back to this game every couple months and have a blast like it was the first time playing it.
There's even a 3D version of it on Virtual Boy called Mario Clash. Tons of fun there too.