I'm mostly looking for completely new games which use the engine of the original but make something fresh and interesting from it. New graphics, new world designs, new music, new enemies and bosses, new items and game mechanics... that's the sort of thing I like in a ROM hack or game mod. For example, I loved the idea of the URA Zelda Restoration before it was cancelled:https://www.youtube.com/watch?v=fQHCRESHtaQ
Hence Project Beta Triforce is exactly the kind of thing I'm looking forward to:https://www.youtube.com/watch?v=-kehj0S5_IM
And that sort of 'change everything to make a fantastic new game' mindset is one that's going into Mario's Nightmare Quest, my own SMW ROM hack. I'm trying to make a Mario mod that feels like it could be a whole new game for a (perhaps more powerful) system. It's why I love the Second Reality Project games and what not.
Challenge hacks I'd like more if they knew the difference between 'hard' and 'unfair'. Too many ROM hacks think challenging means 'cheap to the point of needing constant save states and rewinds' and throwing traps at you that you can't dodge without being psychic. For example, this is an example of a Mario ROM hack which was just utter and complete unfair bullshit:https://www.youtube.com/watch?v=w7cPS2cerFM
It may be 'hard', but that's at least partly because you literally can't see what kills you. And while it's an exaggerated example (in my opinion, the most unfair game of all time), it illustrates the problem with a lot of hard hacks and games; difficulty done in a cheap way for the sake of being infuriating rather than fun. I avoid most 'challenge' and 'kaizo' games because they're closer to Battletoads than say, Dark Souls. The former is trial and error, the is 100% based skill based.
I would play more hacks that fix games if I was a fan of at least one broken game to begin with.