I finally worked up the motivation to go through the companions questline. As I figured, it was really mediocre - just a ton of dungeon crawler-type missions for the same item repeatedly. I suppose you could say the same thing about the entirety of the game, but this wasn't nearly as engrossing as the Dark Brotherhood, Thieves Guild, or even the Mages Guild quest line.
The writing was pretty poor, and there were quite a few things that happened from a character standpoint that didn't really make sense to me. Your character joins the "circle" or whatever almost right away without having done anything, even though it's made out to be some sort of elite/secretive group. I have no idea how Kodlak, a supposedly great warrior, managed to get killed by a bunch of farmers with butter-churn sticks (the Silver Hand) when all he ever does is bunker down in the Jorrvaskr cellar. The motivations of secondary characters don't really click, such as Vilkas randomly refusing to do anything in Glory of the Dead.
By the way, Glory of the Dead is the most hilariouly anti-climatic final guild-quest I've ever done. Weak enemies, a one level dungeon, no boss fights, etc, etc...
Anyways, continuing on.
The guild quests are always kind of dumb in the sense that you go from guild applicant to leader in like 5 quests, but the Companions hit a new low for this. I didn't feel like I accomplished anything significant at all, and there's not really any reason for my character to be the Harbringer by the end except for the incompetence of everyone else.
I did this quest at level 55 or something and it was clearly a level <10 quest-line, so maybe I'm being a bit unfair. It just seems like very little effort was put into the Companions compared to Oblivion when you actually deserved every promotion you earned in the fighters guild.
The story gets a D in my books (C is average). Aela's legs are the only redeeming quality.