Why couldn't GOG have done all this BEFORE releasing it? It's like they didn't test it at all. Ultimately it will cost GOG sales because of all the bad reviews mentioning the mouse speed and other problems.

I installed the latest version from GOG last night and played on Win10 with zero issues. I was using a Bluetooth mouse and didn't change any settings.
I own a physical copy and have seen these issues in the past (among several other nasty ones which appear to be fixed in the GOG version) Going to try on another computer later and see what happens.

It seems to me from everything I've read is not the OS as much as it is the mouse and more specifically the mouses polling rate... is your Bluetooth mouse anything fancy? or just a basic Bluetooth mouse? I have a Corsair mouse with a fast polling rate and the game is unplayable for me unless I install the Corsair software, which I don't want to do just for one game

Yea I was able to confirm it is the mouse.
I tried it on my main desktop which has a USB Intellimouse (https://www.microsoft.com/accessories/en-us/products/mice/microsoft-classic-intellimouse#specsColumns-testCarousel) and I there is a definite deadzone/input threshold there. Small movements don't seem to register.

I generally play older games on a Surface Pro 3 instead (3:2 screen makes them look great), which is what I used last night and I'm using a Surface mouse ([url=https://www.microsoft.com/en-us/p/surface-mouse/8qbtdr3q4rpw?activetab=pivot:techspecstab]https://www.microsoft.com/en-us/p/surface-mouse/8qbtdr3q4rpw?activetab=pivot:techspecstab[/url]) Both the trackpad and the Surface mouse work fine. Plugged in the Intellimouse and had same issues as the desktop. From the specs, the Bluetooth mouse supports a higher refresh rate, although I can't seem to find anything that'll show me what it's actually set at right now. I have a few other mice laying around that I'm going to try.

If they did a hotfix, it did literally nothing about this particular issue. Polling rate and dpi changes have no effect whatsoever. The game either arbitrarily accepts your mouse as the Chosen Mouse, or you're screwed completely and cannot play this game.

I plugged in a $9 Logitech mouse just to test and the game worked flawless... old school game needs old school hardware ;)

Yes! Time to dive in now

Yep, mouse is good speed now.

It's much better this time, but the issue is not fixed, only mitigated.

There is still considerable lag, but at least the mouse does not skip movement now.

It still does not feel the same as under Wine where there is no lag at all.