I've not played any SNES hacks, mostly because I don't have the means currently.
However, the guy at the local game store tried to sell me a repro copy of "super Metroid zero mission", claiming that it's basically Zero Mission for the SNES. After doing some research...I really don't think that's the case. A lot of background graphics were changed & probably the map, but not much else. They couldn't even be bothered to hack Samus' sprite.
That's really what deters me from most hacks. I know a lot of labor goes into them, but a lot of times they just seem like an afterthought. Like, "oh, you like this game? Well we switched around the graphics & level layout so you can have a TOTALLY NEW EXPERIENCE with it!"
The best hack I've ever played/owned is Metroid Mother on the NES, which uses improved sprite art from the MDBtroid & 'Roidz hacks, as well as a mini map & the ability to stack beams and save your game in place of the password system.
This is all my personal taste, though. I know lots of people who'd probably jump at the opportunity to play through Super Metroid or Mario World with alternative levels/difficulty.