What does unzip say?
I won't be buying Shadowrun: Hong Kong until a sale brings it down to $5 or less, so I can't investigate myself, but give my script for extracting makeself archives a try. It should at least split out the contained archives so you can investigate them further. (rather than relying on unzip to ignore everything but the first Zip archive it finds) https://github.com/ssokolow/makeself_safeextract
End-of-central-directory signature not found. Either this file is not
a zipfile, or it constitutes one disk of a multi-part archive. In the
latter case the central directory and zipfile comment will be found on
the last disk(s) of this archive.
unzip: cannot find zipfile directory in shadowrun_hong_kong/gog_shadowrun_hong_kong_18.104.22.168.sh,
and cannot find shadowrun_hong_kong/gog_shadowrun_hong_kong_22.214.171.124.sh.zip, period.
Extracting using your script works, but that's not really something I want to keep doing for all my Linux game back-ups.
The unzip method still works for Terraria though, so I guess they changed something with this new one.