It sounds like it could have came from the original game, but it also feels a little bit empty. I think switching up the rhythm a bit or using the different channels to play off each other might help with creating a stronger feeling of movement, which I think the original OST has a lot of even with the limitations of the NES soundchip.
Rhythm aside, I like the melody! The sounds really do fit the underground level well, and I think the lead up and follow up from the original mario theme was cleverly done!