I think I'm going to have to replay Boulder Dash in the original game, because I swear the boulder is faster in N. Sane Trilogy than it is in the original. It just catches Crash even on seemingly near-perfect runs after the checkpoint with the TNT near it, and I don't remember even having much trouble with that level in the original. The game was hard, but I don't remember that particular level being hard.
Other than that, at least the first game was an excellent remake. Analog controls felt really strange in the first game, so I had to switch to using directional buttons, but after that, I couldn't even notice any difference for the most part. I think it's still slightly less responsive than the original, but it's really close. And I could finally enjoy the bonus levels as well! I have no idea how anyone could have completed them AND collected all boxes in them in the original game, considering you had only one try per level run. But on to the next two games next, having completed the first one!