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.

MD5:
77cc33954337867e85fba1c7d518925f gog_the_witcher_2_assassins_of_kings_1.0.0.4.tar.gz

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 GOG Wiki page.

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.