There's two big things I really don't like about Sky Defenders. First, the game is basically a reskinned clone of the much better Tilt to Live, so if for some strange reason you still haven't played that one yet, go ahead and download the original and see how this "reactive shooter" genre is done. The second issue I have with Sky Defenders is that the game depends heavily on Facebook integration, so much so that when it first starts up, you're asked to log into Facebook right away, though you can still get into the game by hitting a small, gray "Play Offline" button. I really dislike being so pressured to be social -- maybe that's a reality for the developers, but if I was just coming along to this game without knowing what it was, I probably wouldn't have gotten any farther than the Facebook login before I gave up.
All of that said, there is fun to be had here, especially today, as the game is currently available for free. You play as a superhero, and just like the aforementioned Tilt to Live, you use the tilt controls to slide around the screen, grabbing and using powerups against waves and waves of invading robots and trying to score points inside a time limit. The graphics are definitely colorful and polished, and there are quite a few different powers to try and a nice bit of depth to gameplay. There are freemium powerups to explore as well, but they come across as very spammy. Fortunately, the app just had an update that upped the amount of credits you earn just by playing, which makes the powerups a little more useful.
Of course, most of that is sadly "borrowed" from Tilt to Live. But if you really love Tilt to Live and could use a little different spin on things, Sky Defenders is a free download right now.