Amazing!
Aside from some slight differences from the original version (which I think are pretty common), there are a few glitches, but they don't affect the overall gameplay:
ALL: Mushrooms and flowers appear so fast that it's difficult to break the brick next to it immediately after hitting the 1UP mushroom in 1-2
1-2: Hidden bricks (9C?) show up as ? blocks
3-1: One of the pillars at the end drops straight down and a 1UP sound effect is heard, after which it gets stuck into the pillar
Update: After retrying, I found out that it was a glitch in bgb after reading savestate, I'm not sure exactly why, at the moment I think it's a issue on the emulator side.
Update again: it's not a bgb issue either, I'm updating the correct version of bgb and savestate is functioning fine. Very sorry about that.