Never under estimate the value of a sucker punch.

Indeed. A good sucker punch is invaluable. It's 90% of the reason why sometimes the surprise round is the *only* round.

After the first couple times I OHKO'd or ORKO'd an enemy during the surprise round, letting the party sneak forward without an alarm being sounded, the GM started putting us into a lot more twisting corridors rather than wide open spaces.

I can't imagine why.

And suddenly you realize that a few of these guys have class levels!

Or, you know, Nat 20

Can't speak much for DnD, but Weapons of the Gods has the 'unparralelled attack', which can ONLY be defended with an unparrlelled defence, otherwise it's gonna hit, and hit hard!

A good way to mess up the party if they haven't been investing in defensive kung fu.