D&D 5E Spells that turned out to be a lot more powerful than you thought

[FormerlyHemlock]

SLEEP. The "no saving throw" aspect makes it almost never a waste of a slot.

Also a big fan of Hypnotic Pattern. It requires a failed save, but it affects a large enough area that you should at least be able to land 2-3 goombahs with it.

Tangent: I love it too, but unfortunately my DM loves to use undead, and he loves to make undead immune to mind-affecting magic and illusions of all kinds (and resistant to cold, and with permanent life drain, and probably other things I haven't figured out yet).

But in RAW it is a terrific spell.