One of the first things I did after I bought my new Android phone was to install Strikefleet Omega on it. It's by the same people who will, eventually, release Shadowrun Returns. I'm pretty happy with Strikefleet Omega so far. The game concept is similar to Battlestar Galactica; a bunch of bad critters have launched a surprise attack on humanity, and you are in command of the lone surviving human space fleet, warping from star system to star system and fending off increasingly dangerous hostile attacks.
The game starts pretty simple; the bad alien ships fly in from the edges of the screen, you tell your starfighters to go kill them. But then they start layering in complexity; asteroid mining, and extra ships you can warp in as reinforcements, and artillery strikes, and different flavors of bad aliens that require different tactics to destroy. It's an entertaining little "I have ten minutes to kill and I have my cell phone" game. The story is pretty generic, but the character art is well-done, and there are a few little in-jokes for the fans (like star systems named "Plissken" and "Dunkelzahn").
It's a free game, supported by microtransactions, but the microtransactions aren't terribly offensive. You can buy Alloy and MegaCreds; Alloy is used to buy new ship types and to upgrade your ships, and MegaCreds are used to buy perks (special advantages like increased XP or increased fighter damage), to buy special ship types, and to pay for firing your flagship's Deathblossom, a superweapon that kills everything on the screen. The rates they're charging seem kind of expensive for what you get, but so far as I can tell, you can play the game just fine without spending any real money. You earn Alloy during play, so you'll be able to expand and upgrade your fleet just by completing missions. You don't earn MegaCreds past the initial 10 you get when you install the game, but the game is perfectly enjoyable without the premium ships and bonus perks. (You get to choose one free perk every mission anyway, so you're not entirely cut off from that part of the game). It's a shame that you have to spend real money to fire the Deathblossom, but you can think of this as encouragement to improve your play so that you don't have to rely on it.
Overall, well worth my download time, and I recommend it for Android and iPhone users.