Good, but...
...I don't recognise the theme from Metroid 3, because I've never played it! But, it would appear they used exactly the same theme in Metroid Prime for Magmoor Caverns!
So, going on that, I love what you've done with it. It sticks close to the original, but it has enough different about it to feel new. Well balanced, and captures the real essence of Magmorr Caverns, and, I assume, Lower Norfair.