I had fun with Heat Metal a few times back in the day. On the rare occasion I had a target in metal armor, or for ye ol' "creative" uses, and, rarest of all, actually, for the 'mass disarm' (though, honestly, at 2nd, you needed cure light wounds in the slots, an by the time you could skimp on those, the kinds of enemies that would all be holding non-magical metal weapons were kinda off the menu). Still, potentially very fun, if hightly situational (though really, what wasn't) spell back in the day.
The 4e version made a bit of sense for a hafted weapon like a spear, but it working on light/heavy blades was pushing it. The offensive use, as well, would've been a nice touch, because controllers, not just wizards, were supposed to be a little versatile.
5e version has 'fast combat' written all over it. No warm-up, higher damage, upcast for just moar damage. Stronger, vs one victim in armor, certainly.