A black MS-Dos like screen pops up, writes some stuff quickly (did not have enough time to remember or read), and disappears. The only word i caught was "WeiDu". After googling, i found out this is about mods. What the hell, did gog incorporate mods into the game? What's happening here, can anyone clarify? (most probably, this thing is at fault for my crashing of the game, because i am sure as hell older versions, especially of the old gog installer, did not produce such a pop up at the end).

It's a fix called "Force DirectDraw Emulation". Seems like it's installed at the end of all Infinity Engine games.
You can check WeiDU.log in BG2's base directory for a bit more detail.
Also, if you think it's the problem, I'm pretty sure you can uninstall it through "setup-ddrawfix.exe". I haven't tried it myself, though.

I searched for ddrawfix and found this, too. Might help.

That's just GOG installing by default the (DirectDraw fix), and, unless you have very old hardware, that's should be good for you. I doubt that's what causing your issue, but to be sure, you can try uninstalling the mod or reinstalling it and selecting a different option. To do it, double click on setup-ddrawfix.exe in the main game folder and press u and then press Enter to uninstall or press 2 and then press Enter to try the second option. See attached image for reference.

Edit: ninja'd by Poggle :)

Thanks for the replies. Will try and see.

Also make sure DirectX 9 is properly installed. Download the DirectX end-user redistributable from Microsoft, extract it to a separate folder and run dxsetup.exe.
http://www.microsoft.com/en-us/download/details.aspx?id=8109

Aqrit's DDrawFix for Infinity Engine games is here:
http://bitpatch.com/ie_ddrawfix.html

Worse. After uninstalling the Weidu DDRAW fix, now game always crashes with black screen, every time i do a new game in multiplayer. Alas, THIS game, without import/export and multiplayer, is a no go.

Damn it all. I used the Wine direct thing. Seemed to be working, too! Yet, after some time, game becomes corrupted again! C++ runtime error, upon IMPORTING characters! Even the PREMADE ones! It wasn't the Direct Draw mod at fault, after all!

What sort of calamity is that? Now, i need to uninstall and reinstall the whole game, each and every time i need to import even one bloody character!

Too bad, probably thing is headed towards the permanent uninstall and digital dust collecting on digital shelf... Grrr, and i wanted to be occupied by something good until february...

You can always try submitting a support ticket. They'll probably be able to give better information, and if they can't solve the issue either (and you bought the game fairly recently) they'll give you your money back.

Even if gog had been at fault, i would never ask for a refund because i love them, i support them, and i like what they 've been doing round these parts, minus of course the removal of titles for sale here and their permanent transmigration to that wacko-Steam.

That aside, with GoG's, i own 3 different versions of the entire BG saga. And i have a collector's mindset, anyway.

Well, now you've made me feel guilty for suggesting it!

Submitting a support ticket might be a good idea, though. They've been able to help with the all issues I've had with GOG games.

I have a sneaking suspicion that this may be something to do with your antivirus or security software. Try quitting your antivirus completely (don't just disable it), start a new game (NOT in multiplayer), and see if there is any improvement. If this helps, you might want to reconsider your choice of antivirus.