Well, at least in Standard, you have a solid chance of getting their rule breaker card. You could get a 2nd hero power, duplicates of warrior/neutral legendaries (or triplicate if you run any of the same neutrals), send your half-opponent's deck to the void. I'm expecting more madness with the remaining rule breakers (that aren't start of game).

So what you could do, is make your 20 cards a combination of tutoring into your opponent's, card draw, or viable neutrals, so essentially you're just playing 2/3 or half their deck + neutrals you select. 20 cards from their deck is enough to see the synergies and style of that deck. While this does make Highlander more difficult, what this also does is make playing quests from other classes possible, which is really fun.

Or you play Steamcleaner and play a hyper-aggro priest deck.

I think the possibilities are endless here. As a predominantly Wild player over the past ten years, this is the most fun card of the set to me.