For a one man production (more or less), it's absolutely amazing. I have my hunches regarding who coded it (as this person I am thinking of has created some other amazing things for the SNES and I *believe* they may have been directly tapped by Nintendo to code things for them in the past - which would further lend the need to remain anonymous), but whoever it is, they are stunningly talented.
The "mario physics" may not be 100% faithful to New Super Mario Bros or Super Mario Land, but Super Mario Land physics (and general game design) tend to make it a bit of a black sheep of the Super Mario 2D platformer series, but whether it's the original on the GB or this home-brew masterpiece, both are great.
I wholly recommend any Super Mario fan grab a copy of this and fire it up in the latest BSNES to at least give it a play through.
If Nintendo were smart, they'd track down and hire the coder to deliver this as a commercial product. There definitely would be a market for Nintendo-approved SNES cartridges for a "new" SNES Mario game.