MUSICS (9.5/10): Great use of musics here. You almost didn't repeat them, what created a nice and original atmosphere for each level. Besides that, they are all good.
GRAPHICS (10/10): I assume you had a lot of work on graphics. Just like the musics, you were very original by using them without repetition. Original musics with original graphics for original ambients. Good one.
LEVELS (6.5/10): Like it was already said, I agree you made simple levels which resemble the original SMW in difficulty. Savestates are not really necessary to beat the game, and that's a good thing. I judged your game really good until the second castle. After that, I realized your levels were almost the same. I mean, your level style almost don't change from one to another. It's just a different scenario with different enemy sprites, but the base of the level is the same.
It's something like this: You start the level, you enter in a huge block (not literally) full of enemies, then you leave this closed area and the level ends.
Also, you really overused the very same custom blocks from the beggining until the end: ON/OFF passable blocks and enemies-only passable blocks. Several times you must go to one point of the level, activate a switch and then return a good way back to proceed on the level. After the fourth time, this gets annoying.
Many times, you replaced enemies with different sprites to match with the scenario you created. That's a cool idea, but is also repetitive, because you are always facing the same challenge with a different face, nothing else. This mainly happens with Pokeys and boucing footballs. So, what you get here is basically playing the same level over and over. There is almost no surprise on the game.
Another problem I noticed. Sometimes you named a level after the enemy, like Chomp Ruins, Goombas at Work and Starlight Path. On those levels, you will only face several replaced enemies with Chomp sprites, Goombas and several replaced enemies with Star sprites, respectively. Like I said before, there's no surprise.
I liked on your levels that you really paid attention on situations you could get stuck. You were good using invisible blocks and stuff. And your puzzles, though repetitive, were well done.
I praise your mix of scenarios, combining various elements from different Mario games and creating new things with classic stuff. You are good at this.
Your special levels are indeed special. Didn't see anyone making this before.
Pointing some levels:
-Snail Garden: You created here an amazing pacific atmosphere, like if it was indeed a garden. Really good job.
-Mild Mountain: Seems like an interpretation of wild life, without the interference of a tyrant who wanna rule the place. Good.
-Little Reef: It's a simple scenario, but is something I think I never saw before. Good mix.
-Castle 4: There's a bug on the boss battle. If you go to the screen corner, the boss will walk outside the screen limit and the level will end.
-Wonderland: Find funny how wonderland for Mario is a place full of mushrooms.
-Toad Advice: This was disturbing. A secret level with such useless information, just to make you complete the past level again.
-Hot Beach: The first hole is a cool one.
-Final Fight: This level is ridiculously small compared to the graphical presentation on the overworld. And the final boss is far from being a good last challenge. Sorry to say it wasn't interesting at all.
OVERWORLD (9/10): It's well done, except it has almost no secrets.
STORY (7.5/10): You followed your plot by placing different treasures around the levels. But that alien at the end is just senseless. Why is he there? Why he uses Bowser's army to attack Mario? What he wants? Is he using his army to collect/steal treasures? Nothing was explained.
FINAL NOTES: The game is good, but not exceptional. You are really good ar creating different ambients and scenarios for the game. In this point, this game may be on the best ones I have ever seen until now, but you focused too much on that and not on level design. That was a bit disappointing. But in overall, you do have a great potential to make hacks.
The issues about levels can be just my opinion. I do recommend this hack.