Like others have said, I definitely want the lynels to make a comeback. I also want ball n chain troopers to appear, but as a more common enemy, not just a miniboss. And I want them to be humanoid like in the 2D games, I didn't really like it's lizalfos look in TP. And of course I want both iron knuckles and darknuts to appear, but I want them to be more common, because I don't think there were enough darknuts in TP.
In general I want a lot of knight-like enemies to appear, because they're usually the most difficult. Imagine fighting an iron knuckle, a darknut, and a ball & chain trooper at the same time.