Awesome game but there's no way to aim and fire if you have a single button trackpad. (Two fingers is right mouse button, but there's no way to then click with the "left" button.)
Oh yeah, that's true of a touch screen too (it's almost possible to play on phone in browser). For what it's worth you can beat the game without aiming so long as you don't pick up the splitter gun.
Thanks for the feedback. I've logged an issue but we're not expecting to push an update in the immediate future.
Just letting you know this has been fixed in v5. Added spacebar as a secondary aim button.