2-5: Looks neat. I hardly ever see the SMB2 sand blocks used in hacks (at least, these days).
2-Fortress: Looks good, and that's not a bad Layer 3 background either. (I'm not sure how suitable lava is for a pyramid, but...whatever.)
2-A: Seems okay. Not as interesting-looking as some of your other levels, but it ought to be decent.
2-6: The main thing that caught my eye here was that sunset gradient, which looks very nice indeed. The rest should be good.
2-Pyramid: Neat darkness effect. And I thought I was the only one who used anything like that...also, I don't know what you're using for it, but I could try debugging it if you want.
2-Castle: Decent palette here and looks overall good, though I'd make the outlines on those spikes stand out more.
3-1: Looks like a good introduction to the world (though I still don't think your "classic style" graphics look as good as most of your other tilesets). Also quite liking that submap.
3-2: I'd always thought those sharks looked weird, especially the vertical ones, but that's not your fault. This one seems to be designed pretty decently, though if you're going for a SMAS feel, why not use SMB3's Layer 3 water graphics instead of the original ones? Also, now I want an entire level similar to that cave section, because it looks neat.
3-3: It...certainly is an underwater level?
3-4: I'm not sure the barrels
quite fit with the SMB3 graphics, but it otherwise looks good, if a bit hectic for World 3.
3-5: I like the idea of this one. Explosive-based levels tend to be pretty cool.
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I'm working on a hack! Check it out
here. Progress: 64/95 levels.