I'm experiencing quite a bit of mouse lag in this game. Doesn't matter what resolution I choose, fullscreen or windowed or renderer, it's always the same.

Is it just me or is it the same for everyone?

It is typically linked to one (or both) of two things: (1) having "enhanced precision" or the equivalent setting turned on in the mouse control panel and (2) running Logitech's proprietary mouse program (I'm blanking on the name). Could you try turning those off and see if it fixes things?