Well that's my thought too, Wulf. Alertness becomes THE most important feat in the game, and everybody would have Spot and Listen maxed out, even cross-class, just to keep from getting hit with that surprise round.
What I DO like is that it's reasonably transparent to the HP rules while allowing you to model quick, dirty ambushes and long-range sniping.
As you say, however, it's a small change that becomes horribly pivotal. And, because the PCs get into more combats (and thus have more chances to be surprised) it's much more deadly for them that way.
It's a war-themed game, however, so I want to keep lethality high and really have them keeping their heads down, along with rewarding good recon and long-range tactics by keeping OUT of surprise and being able to hit from afar with surprise and take down a critical objective with one round. Instead of twenty.
I'm really liking my "all criticals force MDT" rules ... with Grim Tales I don't have to confirm every critical on the PCs if I don't want to, so I don't have to worry about constantly dropping every PC with low Fort, but it allows the PCs to drop even high-con critters and NPCs with small arms on a good shot.
So I'm thinking of implementing it on the surprise round ... making lethality potentially high, but not the soul-numbing horror of that hard-to-recover CON damage. The DCs would stay low (at normal damages) but still keep that fear-o-God in ya.
--fje