Implosion - Never Lose Hope Full Version $2.67 (through IAP) @ Google Play

Missions 1-1 to 1-6 are free to play and the remainder are unlocked with a one time in-app purchase of $2.67. It's quite a saving as it's usually ~$13.

You have to play the first mission to be able to purchase the game, so it's a good way to try before you buy ;)

Rayak have always made excellent quality games and I've been a big fan of Cytus. The reviews are postivie on Google Play and an indepth review of Implosion is available here

Bringing AAA console gaming experience to mobile devices.

Twenty years after the fall of Earth, the remnants of the Human race are once again faced with extinction. The time has come to justify our existence. A mysterious life form known as the XADA squares off against humanity's last weapon - the War-Mech series III battle suit.

Features: Stunning console-quality graphics, first-class voice acting and Hollywood-grade audio production. Full orchestral scores masterfully mixed by Grammy Award winner and "The Lord of the Rings" trilogy engineer, John Kurlander.

The most intuitive touch user-interface seen on the platform.

A vast arsenal of super-tech weaponry at your disposal, upgradable via the streamlined ARK Kernel system. Become the ultimate fusion of Man and Machine. Ensure the survival of the species.