So I got into the Thailand regional release for this.
It's a game built on the unreal engine and it's not bad at all. The controls are really intuitive and with auto fire on it's super easy to get yourself started with a bunch of kills.
Then the competition starts to get interesting once you pass the first 10 levels. Then it pays to review your control setup to customise the best play style for you .
Bullet Angel is probably one of the cleanest looking smoothest running CS clones I've ever seen on mobile.
I'm giving it a 4 out of 5.