Well, I was just gonna' pass on by, but I tend to favor hacks in which Luigi gets a chance to play the leading role and I also noticed that there's no extensive critique in this thread yet, so here we go:
Level 1 looks pretty flat, honestly. As a SMB3 hacker, I understand it is the nature of that game's plains graphics to be level and flat, but that's all the more reason to try to find ways to go wild with them. Screen #8 in particular jumps out at me the most in regards to this observation: that one screw block just seems way too large to the point of being uninteresting and possibly even coming off as a cheap filler. There are also several places where the ground tiles seem too high; I know that telling you differently is contradictory to my initial point, but those particular blocks look extremely odd when they take up more than two tiles vertically.
Level 2 is great. The passageways are very busy in each screen, and the difficulty seems to be a noticeable bump up from the first level along with a dash of exploration. The Yoshi's Island cave background meshes very well with those SMB3 cave foreground graphics, as well, and I'm happy to see two very different graphical styles working great with each other. My only complaint is the HDMA gradient: while it does look neat and it does add to the feel of the level, it seems kinda' shabby to let it cover the status bar. If this can be addressed, I believe it would be for the best if it went under instead.
I don't really have much else to say about the other screenshots, since you've admitted that they were made earlier in production (which is usually indicative that they'll be tweaked or scrapped), but do try to keep the graphical style consistent in your hack. The impression established from the first two levels' screens is quickly shattered when seeing the lighter, washed-looking graphics and palettes of the grassy stage with a mountainous background. If you keep those graphic sets, might I suggest adding a black outline to increase stylistic consistency?
This shows some real promise! I do however agree with what Mineyl says
Looking through the video;
0:09 - I assume those are munchers? Is there any reason we have gold and green ones? And aren't they a bit much for a World 1-5? Or is your hack supposed to be on the difficult side?
1:06 - What is the point of the star? The next area doesn't have enough enemies for 1ups... it seems a bit pointless really. Ironically, I think its one of the best parts of the level (without a a star of course)
1:33 onwards - The blue breakable blocks seem like they have nothing to do with the level. Putting them there just slows you down, they don't go with the rest of level (unless they can be used elsewhere that the video doesn't show) and clash with the rest of the (frankly brilliant) pallette
I really really like the level design though. I like how the first half was relatively flat and the second half mixed things up, and OK I moaned about the munchers, but they're not what this level is about.
Wow, I really like how this hack is coming along! The YI+SMAS+SMW Graphics style is one of my favorites, especially in a SMAS-based hack. The layer 3 is pretty sweet (but the clouds look weird without animations, I know layer 3 is ass to animate) but they're still pretty good. The palettes look awesome, even though they are slight golden ones of originals, but they are still <3. The whole thing is totally awesome, keep it up!
-------------------- <TLMB> I use YY-CHR to edit DNA
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Sorry, but the scores of wooden blocks (not to mention the cutoff they cause on the pipes) and the throw block walls (lazy level design IMO) spoil it for me. Your level design and stuff is good, but it feels betrayed by (mainly) the wooden block legion.