Neon Chrome 12+

This top-down shooter is fun and well made. Gameplay gets harder as you finish each level - the levels repeat with more and tougher enemies each time. I'm a fan of the top-down genre so I'm a bit biased. This game will eat your battery for lunch so be prepared. The game offers a lower battery consumption option with the trade off of a few momentary slowdowns as other apps take control. I've experienced a few glitches such as my player getting stuck in a corner but that was only once. Loot tends to get stuck in beds so wait until they move away to shoot them. My one major complaint is the cut scenes and voice overs get very, very tedious after playing many levels. Please provide a switch to disable them!

Get Xenowerk, Space Marshals, Space Marshals 2, Halo Spartan Assault or Halo Spartan Strike instead. Like Neon Chrome, all five of those games are twin stick shooters, but all five of those games are vasty, vastly better in every way (fun, graphics, controls, setting, gameplay, enemy types, enemy variety, immersion, animations, solidity of combat, weapons, story (for Space Marshals 1 and 2)), presentation, and you can buy any three three of them for less than Neon Chrome costs all by itself. At 99 cents, Xenoworks is 10 times the game and ten times the fun Neon Chrome is, and it's 1/10th the cost. You can get both Halo games together for half the cost Neon Chrome is alone, and both are way, way better (the only thing the Halo games are missing is the ability to level up your character). I've played Xenowerk for hours and plan to play it more (it's a fantastic game that's an absolute steal for what they are charging); I've played Neon Chrome for about 30 minutes and had to force myself to keep playing after the first couple in the hope that it would get better (it didn't).

Xenowerk, both Halo games and both Space Marshal games also support external controllers as well. All five games have great touchscreen controls that felt better to me than Neon Chrome, but all five are even better with an external controller. Neon Chrome should at least support MFI controllers.

While I understand not making the iOS build as robust as the Steam version... it still kind of stinks. This is a fantastic game, and would have only been made better by including online modes.
Don't let the fact that there's 'only' 25 levels turn you off... it's 25 levels for each playthrough... once you beat Overseer 1.0, you move on to replaying and beating Overseer 2.0... 3.0... ect... there is always more challenge to be had. The additional battery saving mode, and extra graphics options allows for smooth gameplay across quite a few devices, all the way back to the iPhone 5. So... if you're running iOS 8 or above, and interested in twin-stick roguelikes... you should definitely dig deeper into this one to see if it's something you'd like. I know it'll never get deleted from my device.