A lot of the reviews I've read have been very positive, most of the negative ones mention it being 3-4 hours but I'm assuming those people rushed threw the main story and then called it quits you can do the same with new vegas itself the main story can be done rather quickly and if that how you want to play thats fine but you can't turn around and whine that you feel ripped off because it was short you skipped most of the content. I don't actually have HH since I'm on ps3 from what a lot of people have posted its just a vocal minority that are whining.
I liked it and really enjoyed the gameplay, story, items, and perks but if this DLC takes you over 6 hours to complete you're doing something wrong...four and a half to five hours max thats including hunting down the unique stuff.