Ion Fury recently hit the Switch, along with other platforms. Unfortunately, it seems that all versions of the game are suffering from a framerate issue that is causing some stuttering. The issue is explained in great detail by Digital Foundry below.
“The game is basically stuttering at fixed intervals, producing something visually similar to bad frame pacing. … The issue relates to a timer. The engine uses a rather complex timer subsystem that differs from anything in a modern game engine. When working properly, the timer will increase by 2 with each new frame. The issue with this current build, however, is directly tied into this. At a fixed interval, the timer will lose this cadence, and you’ll have the counter increase by just 1, for 1 frame, then by 3 to compensate for the missed update. This only has an effect on the world update though – not the graphics rendering – which is why the weapon sprite updates at a full 60 frames per second (30 on Switch) all the time.”
A patch is in the works to fix this issue, although we don't know how soon it will release. That patch will also include support for inverted aiming as well.
Finally, while the Switch version of Ion Fury runs at 30fps, did you know that you can actually play 60fps if you want? All it takes is the player putting in the Konami code (Up, Up, Down, Down, Left, Right, Left, Right, B, A) at any point during gameplay!