Well, I'm happy to report that I can fly this game in Windows 8.1 64 bits under very specific and unexpected circonstances.
One of the good things about GOG is the ability you get to save your installer. In this case, it made all the difference.
So here's the thing : I fought a long time, and failed, trying to play this game until I remembered I had an older version from GOG stashed on one of my many USB HD.
This is important : the version I used is 18.104.22.168 and dates back to 2012. The actual GOG version is 2.0.0.
At first, I ended up with the same issues, but when I tried again the installer in administator mode, things went a lot smoother. I had to set the compatibility mode to Windows XP (SP3) and select 16bits color mode.
And it worked !
I can play training missions and campaigns though some effects are not as good as they used to be (transparency, clouds layers, and whatnot.). The antialiasing also have a tremendous impact on the framerate though I have a pretty powerful PC. But, other than that, it does work !
I find it rather odd that in the process of upgrading F/A-18 Superhornet, GOG actually broke the compatibility with win 8.1.
I hope my explanations can bring some light and help some of you who have tried to run this game in vain until now.
Maybe someone at GOG could take a look at this issue and modify the current installer.
Until then, best of luck to everyone.
Post edited February 07, 2015 by andromedius