Steam just got its first patch:

We're happy to announce that the first update for Z on Steam has been released!

We've taken on board all of your feedback and have fixed some of the major issues players had enountered, including:
Windows XP Support
Swapped default actions of left and right mouse buttons (added inverted option if you preferred them as they were).
Made the minimap appear by default (tap the bottom right icon if you don't see it).
Fixed some issues with mouse responsiveness.
Smoothed out and adjusted the auto-pan scrolling.
Your feedback has been greatly beneficial and we plan to release further updates in the future to fix other common issues people are encountering as well as actual gameplay bugs. We'd love to know what you'd like to see in future updates too, so let us know.

Thanks for playing!

When can we expect the patch to be available on GOG?

Anyone tried the game on Steam yet with the patch?

Yes. Right click scroll is still inverted (.....). Pathfinding is still atrocious. The cursor doesn't change shape when you hover over things. The game looks extremly blurry on my 2560x1440 screen and the scaling is bad. The map still covers a huge portion of the action taking place ,etc.

The graphics are scaled from the original resolution and the game runs at 1280x800 on widescreen displays, so that combination leads to blurry visuals; the developers say proper resolution options will be added in a future patch but for now it auto-detects between a few hard-coded resolutions. Old-style displays (e.g. 1024x768) actually see more of the game area due to the Vert- scaling used for widescreen resolutions.