Yeah, its 20-25 hours. I'm pretty pissed, cuz I thought I'd be able to finish this in a couple days. Now, I'm stuck playing this crap for much longer than I wanted to. I would have been really pissed off had I rented this game, thinking it would only take a day or two to beat. I have no idea what idiot put 6-8 hrs, but they are dead wrong. That's physically impossible to do.
It probably would have gone faster if this game wasn't so buggy. It took me about 45 mins alone just to get that last artifact on Obelisk of Khamoon, since whenever I tried to drop off the ledge, I kept clipping, and falling without grabbing the first ledge. If by some miracle I grab it, I'd miss the second ledge grab. I was only able to get the artifact because I got stuck standing on that second ledge somehow, while clipping it.
BTW, this is one of the most frustrating games I've ever played.