Before "Grace," I didn't think the characters were stupid--they made mostly reasonable decisions about food, shelter, etc--and the plot advanced naturally for the most part. But here comes "Grace," which has a fair amount of plot development born out of sheer stupidity and a lack of reason.
The treatment of the skitter and its surroundings is pathetically dumb. They try talking to it before leaving it alone with Mike and Ricky. Mike, of course, broke ranks in the previous episode from the sight of his son and should be deemed a hot head at the very least. Mike shoving the gun into the cage into the skitter's mouth is the worst, though. Then he leaves Ricky along with the Skitter! It's stupid beyond belief and, yep, something bad happens. Ricky puts the harness back on and might be dead now.
The Pope stuff was bad as well, making characters do something stupid for the sake of being stupid. On a routine mission to recover more motorcycles, Pope smacks Dai and runs off--but blows up the skitter nest with a tank of gas, drawing skitters to Tom's location. It makes little sense why Pope would blow up the skitters when he could have saved the tank of gas, and it's obvious that his actions were intended to advanced the episode forward, so Tom could start shooting again.
I'm sure the the final scene upset some people with the overtly Christian message, but I was fine with it since most people in the US are Christian. And yes, I'll agree that Lourdes is a moron. What bothered me was the sereneness of the scene, the disconcerting ease every character had in saying grace and acting like everything is fine. This unwavering faith really has no tension to it and doesn't worked as a final scene. On the other hand, certain characters expressing their lack of faith in light of the terror they experienced would be both realistic and more dramatic, especially to end the episode.
Score: 7.9/10