yxomoron: Ok, finally everything downloaded, trying to install - bam!
Installation failed with code -3: Checksum Error
Maybe I'm too spoiled from Steam, but FFS... TW3 installation is fucking nightmare!!!
From support page:
Installation failed with code: -3 Checksum error
Solution
File corruption happens randomly when connection issues (even slight ones) occur during a file transfer. This can happen when you download files manually through a browser, as browsers typically offer limited, or no error protection.
We strongly advise using GOG Galaxy - our new application which makes downloading and installing games as convenient as possible.
Besides being very user-convenient, and keeping your games up to date, it offers the fastest download speeds possible, pausing/resuming, and - most importantly - thorough protection against file corruption while downloading.
Just click on "TRY GALAXY", then "DOWNLOAD BETA" and install it on your system. Afterwards, just launch it, log in, and you can install games directly from your Library section.
Once there, you've got two options:
1) INSTALL - this will download a game's files and install it, as well as add it to Galaxy's list,
2) MORE -> DOWNLOAD EXTRAS - this will allow you to download the classic installer files, but through GOG Galaxy, with all its anti-corruption benefits. Alternatively, you can use our legacy application - the GOG Downloader. You can get it here:
http://www.gog.com/downloader After the Downloader is installed, you can start a download by finding the game in your Library, and selecting the appropriate option from MORE -> GOG DOWNLOADER LINKS.
If your browser and GOG Downloader are failing try Galaxy (option number 2).
Edit: Did you get the same problems if you try downloading another game from GOG?