So, more and more games keep having the "enhanced" treatment like the DnD games and BLOOD but that makes me worried.
I searched a bit in the forums and i couldn't find an answer to this, so my question is: if i didn't buy the original game eg. Planescape Torment (which i have but let's just roll with it) is my chance to play the original without hud changes etcera gone ? Or do the new versions include the original as well ?

It depends on a game. But if original/classic version is included with enhanced, it is mentioned on the product page. For example:
Planescape: Torment: Enhanced Edition includes the unaltered original version and the Enhanced Edition in one definitive collection exclusively on GOG.com. (The original version will be automatically added to your account after purchase.)

Thanks for pointing this out, it seems i've missed it. Having said that, for games like Blood it's still unclear (to me at least). On the store page it says "Includes the original Blood and add-ons: Plasma Pak and Cryptic Passage". This i saw before making this thread but does that mean in terms of the actual game, as in it also includes the original version or is it referring to the original in terms of content as in it's the enhanced version of the original+the expansion ?

Blood: Fresh Supply includes the original DOS version as an extra.

Thanks everyone for your responses, you've been very helpful !

Now you simply need a massive sale on free time to play all said games to completion. :D

Yeap, although i don't see one coming soon. At least i have played Planescape Torment. Blood i think will be manageable, it shouldn't take more than 10-15 hours (random estimate, i don't know how big the game is). The Baldur's Gate series and Neverwinter Nights games are another story entirely as i haven't touched any of them. Eh i'm still young, until i have kids i will probably get through 'em. I hope. :P

You finished PST?!? Damn, that is impressive...now if only I could do so.

BTW: Did you finish it with every class/etc or just one time?

Correct me if i'm wrong but from what i can remember the game doesn't have classes per se right ? You just assign attribute points at the beginning and away you go. Anyway i have played the game one time since it's heavily focused on its story. I will probably replay it in the future but not anytime soon since i still remember the plot (i think i played the game 2-3 years ago).

By classes I mean at some points you can choose classes(priest/magic user/fighter/etc) based on talking to certain companions/others and choosing such/to advances as such and the game often treats you differently in various ways with each of them.

Example:(Semi-spoiler) In one case in an old church you can choose to worship the lady ofn pain/etc and become a priest devoted to her and before that you're told she punishes those who do such and sure enough if you choose such a "class" she does do such to you as well.

Also some skills/etc are only available to you when you pick a certain "class".

Ah yes, i remember that ! I leaned heavily towards magic and pestered Mebbeth to teach me all she knows.

I think this thread is perfect for a question that popped up in my head some time again. If I buy an enhanced version, but only want the classic version to play. What happens if this version does not start up? Do I get GOG to help me run it and if it will not run, is this covered by the money back guaranty or does GOG say „only enhanced version has to run“?

There is very little reason to play PS:T with any other character than high intelligence/wisdom mage.

High intelligence maybe(to get the better dialogs/extra dialogs) but mage being the best/near only one to play seems a bit subjective to me. I personally found the priest/etc class to be fun as well, fwiw.

Afaik both versions have to be able to run or else you can possibly file a request for tech support & if that doesn;t fix it then you could likely get a refund.