Clash of Clans fans will find a lot of familiarity in Boom Beach, a similar title from Supercell with more conventional characters and weapons. This tower defense and tower attack game has become popular very quickly on iOS, and now it's available on Android... if you happen to be in Finland or Germany. (A limited geographical rollout is typical for testing.) If you've got access to this early version of the game, have fun: it's a free download.
Boom Beach pits thinly-veiled cartoon effigies of the US and Nazi Germany against each other. The primary single-player game has you commanding troops that storm the beaches of a fictional archipelago, which are basically short, encapsulated base attacks from any real-time strategy game you'd care to mention. Things get more interesting in the online multiplayer mode, where you can both build your own base and defenses and attack the bases of other players. You can also explore the archipelago and dive in the ocean to find currency and building materials.
Like Clans, Boom Beach leans heavily on in-app purchases. We can't test the game ourselves, but the iTunes page for the iOS version shows that it uses the standard in-game currency model. That means that the players you'll encounter online will probably be heavily weighted against you if they've shelled out real cash to upgrade their bases and units.
If you're somewhere outside of Germany and Finland and you can also access Boom Beach, let us know in the comment section.
Thanks, Aaron Hennig!