Yesterday, I decided to give a try on the GNU/Linux port...
First, as some article say, the sound is in a sorry state, the best sound available, OSS4, is not supported by most distros, in fact it is even hated by some, even being clearly superior to Alsa + Pulseaudio...
On the contrary, the default is Pulseaudio, that in the words of their own developer is: "The sound library that breaks your audio", and not only that, but it cause some strange crashes too (some versions of Wine in particular hate Pulseaudio)
But aside from that, most of the problems in making GNU/Linux software are caused by Windows, mostly the non-standard line endings and directory separator (everyone use /, Windows use \, so anywhere in the code that you use "\' works only on Windows, while places where you use "/" works everywhere, including Windows), after some updating of my system (it was a good time I was developing solely on Windows), I just hit the "compile" button on Code::Blocks (that I use both on windows and GNU) and voila! it was done.
Well, sorta... The binary worked, and I can play my game on Linux by plainly pasting that binary in the same folder of the Windows version and then double-clicking it, now what I need is package the binary for the various distros and etc... Something that I have no idea on how to do, because I never did before (before, I distributed the source of my software...)
This proves that if you want, cross-platform development is dead easy and cheap, there are no excuse to not support GNU/Linux and Mac (well... Mac has the issue that you need one, and they are bloody expensive, but let leave this for another day).
So, Kudos to Steam, Doom 3, and the indies from Indie Humble Bundle!