Play-through time?

I bought this game, haven't opened it yet. I'm wondering if it is really worth having or if I should maybe just rent it. How long does the campaign take? Because like I have been very disappointed with single player games this generation because so much money is spent on production value focused on graphics and not making a worthwhile game, like Modern Warfare 2 which I bought and played through the first time in like 10 or 11 hours. I mean WTF that can hardly even be called a video game but at least that game has online. The last worthwhile single player experience I can remember was Shadow of the Colossus and that took me like 18 hours and that was with going around collecting the fruit trees and stuff so around 20 hours of game time isn't bad to me. But since this is probably more targeted for all ages I'm wondering if I'll blaze through this thing in an afternoon and never touch it again effectively wasting 50 bucks or if it's a very rewarding game as the reviews I've seen seem to suggest. I would probably just trade this back in for SSBros since I don't have that yet.