For D&D, it just seems to me that goblin hordes should be something terrifying to everyone. Instead, a group of six mid-level adventurers could probably kick their butt. Most people work around this by including ogres and hobgoblins, but I think it would make more sense that even though goblins are little runts, if you have 200 of them rushing at you, you shouldn't just yawn and tell the mage to nuke them.
I might be able to pull it off if I had a bunch of self-made goblin mages, and a bunch of archers shooting a thousand arrows. It seems kind of goofy, though, as any decent-sized group of humans will have more than enough leveled adventurers to slaughter the little green guys.
I know this would work fine in Gurps or Runequest, but it just bugs me a bit that D&D kind of falls flat on such an obvious situation.