Finished the game today. Steam says 8 hours in total and I tried to talk to everyone I met but didn't max everything out. Quite short for the awesome fun it was...
The gameplay was fun, especially using all your powers! Johnny Powell talking about all the relics was very very funny! However I saw the ending coming from a mile away
Hope there's more to come (SP DLC?) before TDIII is here (or not

). The only thing I will complain about is the length... 8 hours is very short (but it was packed with action and story!) - kinda like WH40k Space Marine... Took me 8 hours too (but was fun as hell!).
I wish the days of 20 hour SP campaigns would be back in more games (like 141h in Skyrim atm

)