This is a great hack you're working on here, and the ExGFX choices fit well with the classic SMW sprites. The level design is good throughout the hack.
However, I found a few issues while watching the video.
This has already been mentioned but in the 1-2 and 1-3, the palettes in the status bar and of the pirahana plants need to be fixed.
At 5:36 (1-3). The screen randomly moves to the left as Mario goes down the pipe. I think this is because the entrance into the midpoint area is so far to th right in that screen, not entirley sure. I just remember running into this before, but forget what exactly causes it.
1-4
At 8:01 There is a missing tile.
At 8:46 the Dragon Coin is on a Subscreen Boundary. Move it lower or higher. Otherwise it gives the player a ton of lives.
At 8:54 Background Tile is missing in the cloud.
1-5
Nothing wrong as I could tell, but just wanted to mention I liked the whole "climbing on bushes" thing.
1-Castle
Not sure if you're using Layer 2 or not, but if not, a background would really enhance the appearance of the level.
That's pretty much all I found. Liking what I've seen so far. Looking foward to more!