Zombie Highway 2. It's a sequel to another similar game.
It's a zombie-themed endless runner that consists of going down a highway in a car that only go forward, with simple but compelling combat mechanics, largely based on resource management but fast-paced. Like its predecessor, it uses the accelerometer very well, which most games neglect. The steering is crisp and precise.
The general theme is you're in a car driving down a highway, through cities, tunnels, and other environments while zombies jump on your car and try to tip it over. Debris on the road can also kill you if you collide with it. You can scrape the zombies off using the debris, as well, or by swiping into a wall. Or you can shoot them with a variety of weapons, until you run out of ammo, whereupon you generally die pretty quickly. As many as four zombies can swarm your vehicle, and two on either side of it can often flip it over. Any of this immediately ends the game.
Games generally last about as long as the usual casual game you'd play while waiting for an appointment or on the bus, and there's also an "expert mode" which is a genuine nightmare mode.
One thing, it has the dreaded microtransactions, but the only one you need to play the game for free forever is to make even one purchase. I have played this so much that I decided to cough up $5 for that. That gave enough of the game's currency to get halfway to the terminal weapon in the game, and grinding got me the best vehicle. So it's not really pay to win if you're willing to grind a bit, and all of the other weapons and vehicles can be unlocked just by actually playing the game.
It can be played totally for free, though, minus the typical bullshit ads in free to play games (they only show up about a third of the time a game ends).
Also I'll note it has its own physics engine, as compared to the usual bullshit of just slap some crap together in Unity and plaster it with wall to wall ads and bullshit.