StingingVelvet: I'm a long time member who considers DRM free to be an important thing, but I am still being driven to get modern games elsewhere. The reason: patching.
I disagree. I actually bought Shadow Warrior here instead of the Humble Store in part because of GOG's patching system (the other reasons being to show clear support for DRM-free games and to be able to further reward the devs if they eventually make a native Linux version). Unless it has changed very recently there are no patches at all on the Humble Store; every update means having to redownload the entire game.
Anyway:
...it's the delay...
I don't really blame GOG for this.
Firstly, GOG has to wait for the developers to send them the updated files and it seems that devs often take a while to send updates to GOG after uploading them to Steam, resulting in Steam users typically ending up with patches before even GOG themselves have the updated files.
Secondly, GOG has to then put together and test a patch; this process takes time. This differs from Steam where (AFAIK) the updates become available for download through the Steam client soon after they've been uploaded by the devs (as there is no patch building or testing involved).
...the frequent need to redownload the entire game again...
"Frequent" is a bit of an overstatement I think. This has only happened twice so far and both times it was because the updates involved were so large that they deemed it more appropriate to just update the main installer. This kind of thing has happened in the past with Steam too, by the way.
I think part of the issue is GOG only providing the base installer + latest update (which has to work on all prior versions since the current base installer), however the alternative would mean ending up with having to download and install a string of patches after a while to get a fully updated game which would arguably be even more hassle. They *could* provide two sets of patches, but then that would mean a lot of extra work building and testing them.
and in Shadow Warrior's case even having to uninstall and reinstall.
I have no idea what you're talking about here; I have had Shadow Warrior since release and I've not once had to uninstall and reinstall to apply any of the updates. Even when they replaced the main installer.