As a bias melee fan, I would just say project M it, but I don't think that will happ en, and if it does, it won't be as good as the original project m or melee.
Anyways real talk, if we want smash 4 to be decent we need these changes:
1. removal of rage, that mechanic is awful and against falcon, he's always at even with you no matter his damage level since everything he has contains so much knockback.
2. change the ledge mechanic. Either A. make it like brawl, or B. keep it, but remove the magnet hands when doing up b moves to reward skilled players at their recoveries or else they get hit from onstage easier, which would also make rage way less of a factor than before.
3. bigger window for dash dancing, it gives characters a good way to approach.
4. little mac's ground speed/frame data and armor need to be nerfed and his air game slightly stronger as to make him less polarizing, and more fun to fight against.
5. removing the untechable spinning animation. I don't know what they were thinking of adding an arbitrary un-teachable situation, but if we complain enough, they will remove it.
6. ROLLING!!! Ok, so we all know that moves get stale when used too many times right? What if rolling did the same thing? Like the more you roll, the slower and more vulnerable your character gets, and the less invincibility frames you get during it. It would work like this, you get 7 rolls until you lose invincibility and the speed of it it similar to charizard's roll animation in project m. Every 10 seconds, you would get one layer of stronger of rolling back. So for example, sheik has rolled 6 times, and is near out of invincibility, she kills her opponent and waits 10 seconds before starting to roll again. She rolls, and it would be her "6th" roll rather than her ****ty 7th roll she would've got had she rolled earlier. This punishes defensive play, and would for glory players something less nooby to rely on.