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From what I hear, the performance was pretty bad... not sure how it could be worse that episode 3 which is a slug fest in certain parts, but it might have failed GOG's standards for release. They do actually test this unlike Steam.

Other than that they might have gotten the build pretty late, one has to remember they are in poland and they manually add each game. Hopefully it will be up soon.
Game went live an hour or so ago and just finished playing it. Feels like they finally got the game optimized! :D