CapnZapp
Legend
This is also too soon to say.Sleep now retains its usefulness throughout the game, due to scaling in higher spell slots--and the fact that it works based on current hp.
If anything, indications are that monster hp scale up much faster than spell slot scaling.
If that is generally true, then spell slot scaling should not be viewed as more than a consolation prize for those spellcasters who have high level slots but no high level spells. (Such as multiclassed spellcasters, who at first blush are "fixed" compared to 3e, but might very well in actual 5e gameplay prove to be borked still, only less borked than before)