I completed all the normal achievements yesterday (minus the DLC) and agree with everyone (except the guide maker) about the difficulty and times listed in the guide. They are wayyyy too low. I would give the game a 5 or 6 for difficulty. If the original is a 6 and this one is slightly easier then let's say this is a 5. It took me 19 hours of playing according to Raptr so I think the time at 15-20 hours would be appropriate too. It seems like the guide creator was an exception to the rule and ridiculously good at the game so their experience may not be the best to judge those two stats on.
With that said I'm excited for the DLC and may pick it up at full price. My hand is cramped from playing the game so much this week so I need a break.