I've seen a lot, ranging from meh, to looking actually really good.

In an older thread I showed you a hack called Mario is Missing Done Right, so now here's New Super Mario World 1: The Twelve Magic Orbs.

From what I've seen so far this one's quite impressive. Even having custom made backgrounds and some original enemies. :)

What are some good Super Mario World hacks that you know of?

I'm still waiting for Super Mario World Central Production 2... But it looks like it's nowhere close to finish. =/

What's the first one like? :)

Well, the first one is great. However, SMWCP2 is looking like one of the best (if not the best) hacks ever. They are using original GFX, original Soundtrack, and a lot of new features. However, it's "in production" since around 2010.

You don't think anything bad happened to the creator, do you?

No, the hack is a collaboration project. Each level, the map, and musics were done by different authors. If I'm not mistaken, over 100 people worked on the levels, but they always had to struggle with bugs, members giving up or even lack of interest. Also, this project is very ambitious (Around 100 levels, lots of new musics, cutscenes, bosses, etc.)

Here, I got some screenshots for you:

I'm in love with user-created content. Modding is probably the best thing there is in gaming.

But this is roms and roms are evil.

Super Mario World hacks are what Mario Maker should've been. They've progressed to the point where it's not just trolls trying to make impossible shit, but actual good levels and interesting ideas, which are more common than not.

Having said that, I really hope SMWCP2 at least has shorter levels than the first one. That hack had way too many levels that just went on and on for several sections at a time without checkpoints, to the point where I ended up putting down save states halfway through out of frustration.

Well, I played the base ROM, and no, the levels are not shorter. However, a lot of levels have two checkpoints, what makes them more reasonable to beat.