A Fun Diversion
With friendly airdrops sending in varied firepower, and nukes that can wipe out an entire screen of enemies, it's a fun game in short bursts. It also looks really pretty, kind reminiscent of the Metal Slug style.
The levels are timed, and they continue endlessly, one after the other. Unfortunately, you can't save your progress. It's designed like an arcade game in that sense, which is my only real gripe with Army Defender. It's a great quick-fix experience, but you can't simply put it away and come back to it later -- you have to start from the beginning each time you start the game back up.
For $2, it's a worthwhile mobile-app-type game. If you're into this sort of thing, it's a good value. But beware you will not be able to save your progress.