I downloaded this game last night, but when I extract it I get the error "truncated gzip input". I just ignored it and installed the patch, all the required packages, but when I run the game it just opens the crash reporter. I can run the launcher and config, but as soon as I run witcher2 it crashes. I am using Xubuntu 14.04 and Nvidia gt755 with 331.113 driver.

not sure if the file I downloaded was somehow messed up? I will try downloading again, but I won't have time until tomorrow.

I am not sure what part of the crash report is important or the output when I run it from the terminal, I can post it but it is rather long. This part looked important though (from the very end of the crash report):
[thread ffffffff][I][0]: Log system initialised
[thread ffffffff][I][0]: Default allowed number of simultaneously open files in the system is 1024.
[thread ffffffff][I][0]: Current memlock limit is 65536.
[thread ffffffff][I][0]: setrlimit(RLIMIT_MEMLOCK) failed, (1) Operation not permitted
[thread 00000001][I][13]: OpenGL information:
[thread 00000001][I][13]: renderer: GeForce GT 755M/PCIe/SSE2
[thread 00000001][I][13]: vendor: NVIDIA Corporation
[thread 00000001][I][13]: version: 3.2.0 NVIDIA 331.113
[thread 00000001][I][13]: GLSL version: 1.50 NVIDIA via Cg compiler
[thread 00000004][W][75]: Game is trying to enable termination on heap corruption. We don't have it implemented at the moment, implement it? This warning will be issued only once per run.
[thread 00000004][W][103]: eON_LoadLibraryEx() couldn't load 'C:\home\a\Desktop\GoG\The Witcher 2 Assassins Of Kings\game\bin\telemetry32.dll', returning NULL!

Looks like there's something missing. I'd also start with re-downloading it.

That's rather annoying. I already tried downloading 3 or 4 times before this and it always messed up halfway through. Will try again tonight though.

Excellent Gydion, the MD5 hash is exactly what averyvh needs. +1
I just haven't had the time to re-download the game and calculate it.
Btw, it'd be also helpful to add it to the game's [url=http://www.gogwiki.com/wiki/The_Witcher_2:_Assassins_of_Kings,_Enhanced_Edition]GOG Wiki page[/url].

averyvh, calculate the MD5 hash of your file with the terminal command:
md5sum gog_the_witcher_2_assassins_of_kings_1.0.0.4.tar.gz
If Gydion's and your file are identical so is their hash. If they aren't, your download is corrupt (or Gydion's ;-)

If that's wrong then a few are corrupt. I don't have a GOG Wiki account. O_o

An aside, I almost don't recognize you with that avatar even if it looks nearly the same.

I checked the md5sum of my game and the result is the same as Gydion's: 77cc33954337867e85fba1c7d518925f gog_the_witcher_2_assassins_of_kings_1.0.0.4.tar.gz

If you got a "truncated gzip input" then most likely you have a bad download.