Comments about Outdoor Research Sentinel Brim Hat:

I got a large and have a 23-1/4" head and it's a bit snug, but I guess I'll deal with it. I guess I should have gotten a size up, but woldn't want an overly big fit either. (even though they are adjustable) Overall it seems to be a good hat, but I haven't put it through any long days in the sun or bug infested woods in the evening.

Small negitives, the head band tends to not stay put or is not situated qutie right if you casually throw on the hat.
Maybe not as vented as it could be around the crown, but I don't know if it would matter if it had more venting or not. (my Columbia hat is vented all the way around the crown)

Pros:
The brim size is not horribly large and stupid looking. Better perportioned looking to most heads I'd say, though that obviously means a little less sun protection, but still seems to have a good ammount. The Columbia hat I am replacing is a about 1/4" to 1/2" bigger all the way around the brim and just looks a bit goofy.

Comments about Outdoor Research Sentinel Brim Hat:

I normally wear a 7 5/8 fitted hat (big melon) and the XL fit perfectly. The hat can be tightened, but it was comfortably snug without adjustment. Very lightweight. After a full week hiking Great Smoky Mountain National Park, my head and neck were sunburn free and the hat had no sweat ring on it. Would buy it again.