If only there were a gaming store that sells good old offline games :D

(Yes the download sucks)

yeah, GoG needs to create a similar type of system that Steam has. Steam breaks the games down to 1MB chuncks. When a patch happens, it basically analyzes the chuncks and just uploads to you the changed 1MB chunks, and if any of the 1MB chunks are identical to another 1MB chunk then it won't download duplicate chuncks, just use the same chunk already downloaded, hence why it is 5GB on Steam vs the 26GB on GoG. GoGs system is just replace whole files that have been changed, and then uploads them to you in compressed format, so it is 26GB because they made a change to the vast majority of the game files.