Maybe I'm missing a lot just reading what's posted here instead of the full books (GL at least, GLC is totally one of my pulls), but Hal doesn't seem quite so Marty Stu as much as a perspective character kind of hazarding his way through each of the new corps.
It definitely wasn't any strength of character that got him a red ring, or gave him proficiency with it. Since red ring slingers are supposed to be mindless, I would think proficiency comes automatically, like their extensions of Atrocitus' power more than individuals in their own right. an, as has been pointed out, he didn't get out of that through any effort of his own.
Now, I hadn't seen him trying out a yellow ring if that's happened yet (haven't read SCW), but I might give him that one for having probably more experience with Sinestro than most other Lanterns. So, calling him a Marty Stu might be a little premature, but we're early in this, so it's still a valid concern.
Something that's irked me is the Red Lantern who escaped on the last page of GLC last month looks way more like the guys from the Five Inversions than Atrocitus. Did anyone else catch this?