I played years ago with Epic-40k patch and it worked fine.
Hovewer, today i found that even with the patch enabled i had the stuttering when using the various movement/shooting overlay.

Luckily i managed to found this other wrapper that seems to work fine:

1)After downloading and installing Final Liberation remove all the compatibility settings from the Epic40k executable.
2)Download DDrawCompat 0.3.1 from https://github.com/narzoul/DDrawCompat/releases
3)Extract it in the Final Liberation folder.
4)Download the movie crash fix patch (fl_highcolor_patch.zip) from http://bitpatch.com/fl.html
5)Extract it in the Final Liberation folder and run the movie crash fix patch (FL_HighColor_Patch.exe)
6)Run the game, it should work fin and the overlay will not make it stutter.

Thank you!!

I was pretty pleased to just get the game to run with the other wrapper people have mentioned, but being able to use the movement/line of sight overlays has made it 100% more fun.

Amazing!
Works perfectly as of March 2022 on Windows 10!
Thank you!

You are a wonderful human, nostalgia here I come :D

Now we need a way to do 1080p

For some reason, if you try to use the 0.4.0 version from the repository, the game will still crash. The 0.3.1 version works like a charm, though.

Thank you!!!

I understand you posted this a long time ago, however I followed these steps as written and after rebooting (for the dll install) the game just crashes upon execution. As soon as it's run, I click Yes for Run As Admin, the screen goes black, and I hear a ding sound of the error popping up behind the app. Eventually I minimize the black screen and the game finishes the crash. I tried putting the compatibility setting back in place but still it does nothing at all. I'm on Win 10.
Event Log entry for the error message is pretty useless, but it shows the app: Faulting application path: C:\GOG Games\WH40K Final Liberation\Epic40k.exe
The error box itself is just a white box with no text / buttons on it.
With no error message I don't know what to change... Any help / ideas would be greatly appreciated.

Just reinstalled it on a fresh install of Windows 11 version 22H2 - Still working great!

IMPORTANT - I had to use 0.3.2 of DDrawCompat.
(Version 0.3.1 or 0.4.0 causes crashes for me after the initial logo!)

Only niggle is having more than one monitor/display plugged in makes the game unplayable, same for anyone else?

Tried the wrapper above and version 0.3.2 removes the lag when selecting the movement / line of sight overlays. Running Win 10 64 bit. Had no crashes after intro fmv initially, just the lag issue. Wrapper has fixed this :)