The Sonic game uses the most vile type of in-app ad. The ad requires you to play Game of War for some indeterminate amount of time. You are made to play it after every stage. I hope Sega changes this, it basically makes their game unplayable.
I'm starting to get to the point where I wish people weren't allowed to call advertising supported products "free." I don't know what other term would be better, but I feel like users are paying some non-monetary cost.
Brainshareware is more accurate but it is a mouthful.