Looked at a few videos. So it’s mainly widescreen, parallax backgrounds, and shadows. Also a level editor (like Mario Maker).

Resource packs basically means you can reskin it. You can play as different characters (but I think they all play the same).

I didn’t see any different level design though, at least not in the actual levels. They showed custom levels. As for the physics, I think I saw a jump that didn’t look right. Like normally if you jump on an enemy, you kinda “bounce” one square up. But I saw Mario (or one of the skinned characters) jump on an enemy and springboard off of it and that did not look right. I do know it’s possible to do it in the base game, but what I saw still didn’t look right.

Honestly in addition to widescreen support, I would really just want controller latency to be addressed. Playing Mario 1 on anything but original hardware feels like it’s ice level physics (like how Mario moved in the ice levels in SMB2-US). I just can’t do it. I used to be great at the game. The latency kills it for me. I’ll still play the 2D Zelda games though. Not Zelda 2, the latency is an issue too often. And Minish Cap, there are a couple boss fights that are way, way harder because of the latency. They were tough on the GBA, but not that tough. Mainly the giant Octorok.