I finally got around to starting this. I'm about 2/3 of the way through. Normally I would blow through a game like this in one or two days playing all day, but I can't play this for very long (by my standards anyway) without getting bored. To me, Reach has just further cemented Halo's status as an utterly mediocre franchise. There is nothing great about this game at all. Of course the Halo fanatics will disagree, but there opinion is usually meaningless since they play so few different games that they have nothing to compare it to. As someone who plays a ton of games of all different types, I say these games are about average.
Are you giving it an average rating based on the overall experience, the gameplay or the story?
Gameplay on Reach is definitely more of the same. I'm playing it because of the story.