Neon Chrome 12+

I picked this up on Steam a few months back, and I'm still playing it on the PC. When I saw it on the app store, I didn't hesitate to pick it up. In terms of content and sheer fun, NC is in the same league as Enter the Gungeon, Binding of Isaac, or Nuclear Throne.

The translation to iOS is brilliantly done, with the controls and aim assist combining to make NC easy to play on both my iPhone 6+ and my work phone (iPhone 6). The only hitch is in using secondary abilities (like missiles etc)... It can be a bit awkward on the larger screen. The devs have implemented a helpful "slow-down" mechanic (game time slows to a craw to allow you to comfortably aim the secondary fire) which mitigates the issue a bit.

There's an absolute ton of content here. Each run is procedurally generated, and you have to complete multiple runs to unlock all the equipment/skills/traits... Of which there are a small mountain.

Graphics and audio are both outstanding, and set the mood beautifully. (In fact, I'd love to be able to buy the soundtrack)... It feels very Shadowrun / Bladerunner / Neuromancer -y.

If twin stick shooters or ARPG's are your poison, give this a crack and you won't be sorry.

Well, that was a waste of money. Opens at 1/4 size with no touch input. Supposed to be compatible with my phone.

I normally don't buy action twin shooters as I find them to be usually too hard and too frantic to enjoy.
Neon Chrome, while at times is hitting the frantic pace, is a twin shooter that relies more on good positing and careful aiming.
The difficulty is excellent giving a good challenge while not being frustrating.
It is a true pleasure to play in both short bursts and longer play sessions.