I fixed a typo there. It should be (after you run cat):

rm pack0.dzip.split*

Yep, we already figured out that post installation script merges three files there, and if you just extract the package without the installer running, you'll be left with those split files and the game obviously can't start properly. So from now on, pay attention to post-installation scripts if you don't use the installer.

Ah, sorry, I misunderstood, I thought someone said the installer didn't work either.

Which unfortunately makes the installer require another 10 GB of hard disk space during the installation. Not very smart. I guess they expect or use dumb file systems which cannot handle files larger than 4 GB. But it still doesn't make sense as the installer is already larger than 4 GB, so an old file system already would fail there.
It indeed does not work for me. But Debian is not officially supported, so ...

Therefore I don't think it's the reason. It has to do more with compression I suspect. I.e. they for some reason don't want to have a huge single file inside the archive. May be it increases RAM needed for compression and decompression? I personally don't care about it much (I have 16GB RAM), but may be GOG triggered some cases which exceed minimum system requirements with that package? Just my guess, I have no idea really. Usually you can limit RAM consumption for the decompressor even for huge files, but that can increase decompression time.

At least the game seems to run for me too now. :)

Would have been easier when the programmers would have checked the return code of the open and dropped a message about the missing file. ;)

Wissaner!

aaaaaa

Not a surprise for me, I had to do something similar for my custom DEB packages (splitting pack0.dzip) because of a filesize limitation with the .ar archives used in these packages.
I’d guess something similar happened with the .zip format used for MojoSetup installers.

I’m not sure about this, but I think that xz-utils isn’t installed by default on Ubuntu LTS.
I don’t know how easy/hard it would be to embed unxz in MojoSetup installers.

Anyway, if they’re going to embed a non-standard archive format (+ unarchiver) in MojoSetup installers, lrzip would be *the* one to go with ;)
http://ck.kolivas.org/apps/lrzip/

Probability of that is not any lower than non default pre-installed packages which they list in prerequisites, such s SDL2 or other stuff :) They can easily add xz-utils to that list. And it's a very useful package to have in general, so it's usually installed even if its not a default.

By the way, installers can check for missing prerequisites and report that to the user instead of exiting silently. Mojosetup and other used tools are open source so GOG can improve them if that feature is missing.

I'm not sure about rzip. Is it parallelizable? Current version of xz is multithreaded already (though the version in Debian is very outdated, I tried contacting the maintainer twice already to no avail).

lrzip, not rzip. lrzip is based on rzip but comes with many improvements.
It’s multithreaded, and from tests I run it seems to beat xz on both compression/decompression speed *and* compression ratio. If you don’t already know lrzip, you really should have a look at the README on the page I linked: there’s chances that you’ll adopt it quickly ;)

Sounds interesting. I'll run some benchmarks (using TW2 files ;)) to compare it to parallelized xz on my machine.

Some previous tests results were posted here (note, that xz I used then wasn't parallelized):
https://www.gog.com/wishlist/site/use_better_compression_for_linux_tarballs_for_example_tarxz

(Also, GOG royally messed up wishlist comments, so it might be hard to read them now).

I just use the global hotkeys control panel to bind that KWin action to F11.

Thanks that worked.