It's funny, I am of almost the exact opposite of Darth Bambrox. I thought that the story was a bit cliche. I wasn't surprised or impressed by any of the twists, as they are similar to twists in many other video games. I would post examples, but I'm following your lead of trying to keep spoiler free. On the other hand, I found the game play and the atmosphere to be the strongest points of this game. I stopped to check out background art, sculptures, scurrying gretchins just barely within reach, orcs who hadn't noticed you yet fighting each other, etc. I thought that the setting and atmosphere were outstanding. I also liked the gameplay precisely because it wasn't your typical "strike, evade, cover" tactics. You must kill to stay alive. I loved being immediately swarmed by orcs from out of nowhere, and not being able to hide and strike.
I agree with you that this game is definitely worth picking up cheep, but not at full retail price at this point. But the reasons I like and dislike this game are the complete opposite of yours.
As an adjoiner, the multiplayer has a bit of a learning curve, as the tactics and gameplay are vastly different to Halo, Gears, MW, or any of the other popular pvp shooters, but if you stick with it and learn the game grinding to level 41 is a lot of fun too. Of course, that means either picking it up new (which will make it more expensive) or buying the online pass. But the campaign alone makes this worth a mid-price purchase.