General about W1 : Very nice world map , I really like all levels so far
1-1 - The bridge is made out of coin-in-brick from the left but the right part is made from bricks only. Is that intended ?
There are also small graphical glithes where You place an edge which overlaps another 'hill'. It's transparent in that spot. It's especially visible in the area with 3rd star coin, makes it look kind of ugly . You might want to create a separate edge with the transparent part filled with the hill's body, if You have any space left in the tileset of course
1-2 - At the beginning of the cave part, there are two holes in the ground, and when You jump into the second one You can see that the one on the left 'is there'; , but when You jump into the first one , You die. I actually thought that there might be a star coin there. It's nothing major, but I'm just reporting. In the next part , half of the screen consists of the ground, You might want to block the camera from 'entering' the ground, so that the actual playfield is more visible. In the section that thereturnofdoritosxD showed in his first video, the right wall is made of wrong tiles WHen I jumped on the first pipe after the checkpoint while being a mega-mario it shows that there's a second pipe underneath it.
1-3 : The part where mushroom stalk connects with the mushroom 'platform' is solid, but the rest of the mushroom is solid-on-top. Is that intended? Also, the stalk from tileset is visible behind the stalk from the sprite itself in the part with big moving purple mushroom with P-switch triggered blue coins. The midway point makes player start at the beginning of the level anyway. The bonus area for Star coin 2 is pretty cool, but I don't know if the used ?-blocks are good choice for 'holding' the vines. ( btw, I love the tileset )
1-T : It's kinda kard for the first world, but I like it Nice and tricky. The timing for the red blocks section at the end of the tower seems to be veery tight though. I couldn't find the second star coin, and Could'nt reach that first ?-switch at the beginning of the tower.

1-T : The second star coin hiding spot is too obscure, and there's nothing that hints that those blocks are non-solid :\ Consider at least placing some coins in an arrow-like shape ( SM64 does that ). Yeah, the difficulty is the only issue that I can think of right now , maybe at least make the red blocks section a bit easier, but it's just a suggestion, obviously NSMB hacks are played by advanced players. You can also consider changing lazy tiling of tower's walls in one part ( just the same tile repeated over and over )
1-4 : I think You should zoom out the view a little bit, because it's very hard to see where I'm going. ( in my first playthrough of this level I didn't find a single Star Coin, because I got lost in the level ) In the bonus area filled with coins ( the one that you access by a green pipe facing left , with invisible coin block underneath ) there's one block missing in the bottom-right corner The bonus area with coins and roulette block ( and an awesome Kirby's cameo ^^ ) has no sound effecs , You probably forgot to set the music for the view. The bonus area at the very beginning of the level is kind of confusing , it's unclear that You actually need to be small mario to acces the room. Maybe add a sign to the tileset with small mario ( You could use a mario from the original NES game, it'd require few colors ). Also , if You access the area for the second time, there's no P-Switch there which prevents Mario from advancing any further and basically traps him in the bonus room - I had to wait for the timer to run out. The shell for the bonus area with star coin 3 is a pain in the butt to get , but I guess it's OK , it's not like it's impossible( i waited for the bahps in the song to actually be able to collect the shell). In the part with lots of those purple mushrooms a few of them don't stand on the uh... ledges? The speed trial is quite cool . The stop-camera from entering right wall at the beginning of this bonus area is placed 1 tile too high. It's also possible to re-enter this trial, but the whole wooden blocks maze is missing , so it's kinda pointless. You could block the access to the trial after 1 try, so that player doesn't waste their time ^^.( it seems like you try to do that, but I accessed the trial anyway... And I don't know what You mean by 'Take these rewards' - I didn't get anything ;(.
1-5 : The green mushroom where the star coin 1 part begins is broken. ( that's it... I ahve to use the editor from this moment on ^^ )
The wall is missing :
The solid tiles that I meant in my previous report (there's more, check the whole tileset thoroughly , small green mushroom is solid instead of solid on top as well ) :

This pipe is really unhinted , I had to look into the editor to find it , add a bit more coins leading to it.

In that area , graphical glitches occur on my DS , someone should test it on their DS because I'm not sure what causes it.
//Wow, I forgot about one more thing , in 1-5 area 2 there are 2 accidentally placed overlaping zones, one of them has no music set and the area has no sounds. You have to remove one of them
//And one more ( hopefully last ^^ ) minor thing. This pipe ( short , red one ) should have the exit entrance set to exit only , I guess.
//And one last thing , in the bonus area with pipes when You are at the very top you can see the background at the top is a bit glitched