15 to 20 hours I guess. It has less main story,I think its 9 sequences while ACII had what....14? 
 
Less story but more things to do in the world

The main story is probably comparable to ACII in terms of length, but you can easily dump 20+ hours into the game by doing side mission, training your assassins, looking for collectibles, buying property, etc. 
If your friend is a completionist, it'll be great for him/her.

Alright thanks. He's not too much of a completionist, but I know that if it's length of ACII than it should be enough.  Once again, thanks!

Great offline experience; you should DEFINITELY get this for him

To date I've spent almost 27 hours in the single player mode.

" The main story is probably comparable to ACII in terms of length, but you can easily dump 20+ hours into the game by doing side mission, training your assassins, looking for collectibles, buying property, etc. If your friend is a completionist, it'll be great for him/her. "

I put more hours into brotherhood than AC2.

ACII had a better plot.  More intricate and better thought out I think, but Brotherhood is still a fun story.  I would peg at around 20 hours.  It has a lot of open world options outside of the memory missions that you can really spend some time on.  100% worth getting.

" To date I've spent almost 27 hours in the single player mode. "

Overall the campaign felt broader and was more full of things to do than AC2's campaign. There's so many sidequests, the assassin recruitment and training thing, etc. I've dumped a ton of time into AC:B (probably 15-20 hours) and still have a few memory sections to go before I'm complete.

If you critical path it, it's ridiculously short.

I thought the actual main story felt a bit shorter, but the game's side-missions are way more numerous and fun that those in II, and if you count them, Brotherhood takes longer to complete.

I say it's the same

" @natetodamax: Yeah I own all of Rome and have all of the single player achievements except for the stupid flags.  I'm actually only at like 60% sync though.  I didn't realize early on how important it was.  "

" @OneAndOnlyBigE said:

" @natetodamax: Yeah I own all of Rome and have all of the single player achievements except for the stupid flags.  I'm actually only at like 60% sync though.  I didn't realize early on how important it was.  "

just get the maps then it is maybe 30minutes running around, not really that hard, I ended it with 76% "