I was just saying that we'd see more freemium action from Backflip Studios soon, but I didn't think it'd be quite this soon. The studio has released its second big freemium title, called Boss Battles. This time, they're taking on the space shooter genre. As you might guess from the title, the game is indeed a series of boss battles, pitting you against a number of different space shooter bosses that can earn you a bounty of gems. Those gems can be used to upgrade your weapons and ship's accessories, and they also serve as currency for your ship's lives. If you need more, you can buy more, or you can earn them as you play.
There is one hitch on this one, and it's that Backflip has included ads in the package -- even if you buy one of the in-app purchases, you still have to deal with ads on the screen. But they aren't that distracting, and considering that the game is free in the first place, the ads aren't too much trouble. The game also offers full Game Center integration, and five different difficulty modes to play with. Boss Battles is available for free right now on the App Store.