Actually it's -
New unit models
3 new guns
new plane
3 new vehicles
2 new maps
15 mission campaign
(thats off the top of my head)
Now before you say that is not enough for 12 dollars, keep in mind that it is content by the developer and supported by them. Since it is an officially released product many players will have it and mission designers can craft for it without worry that players won't have it. In fact the patch release before the DLC is to include low res textures for those players, such as yourself, who don't want to purchase it. Now THAT kind of work from a developer is worth 12 dollars.
It's pretty simple. I work, work gives me money. I give money to BI, they give me content. I play content in a game I enjoy. They stay in business and make more content. Repeat cycle.
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Everybody gets everything they want. I wanted a mission. And for my sins..they gave me one.