You basically get like 2 to 2.5x the stuff in AC. But, even if you don't buy it, it won't set you back that much.
Most new games cost like $60 so think about that for a minute. You're getting the game + additional content that will save you money.
If you're one of the people who are complaining about it. Just remember you don't have to buy it. It's optional. Be thankful that you don't even have to spend money to play the game if you don't want to.