Depends on what the belt is made of, that one looks a little glazed but not too bad. I've noticed on the aftermarket belts they're a bit more plastic feeling/ looking, when they wear they get rather glazed and a bit harder/shinier? (Can't seem to find the right descriptor...) makes me wonder if they use a similar material to timing belts which can look good even though they're worn.. They will usually start developing small cracks that become more obvious over time perpendicular to the ribs, I've seen a couple with missing chunks, but not often. The factory ones seem to stay more supple feeling even after a long time and with cracks in them.
Something entertaining if you're bored is running a pick through the grooves and seeing how many ground up rocks and such get embedded in those belts.