It could be "Times of Lore". Looking at the box cover on Wikipedia (http://en.wikipedia.org/wiki/Times_of_Lore) I see a similar kind of all-caps yellow font against a brick background, like in the title page of the video hint.

No idea what finding 5 CDs in a box has to do with it, though.

... or magicka ?

Googling for arcania fetch quest brings up lots of reviews basically saying that the game is one big fetch quest. Here's one example:

http://badassdigest.com/2013/09/04/game-review-arcania-the-mother-of-all-fetch-quests/

"But what if a game was comprised entirely of fetch quest? What if every single time you tried to advance in a game you were forced backwards and sideways and back again, only to end up on yet another fetch quest? Wonder no more, dear readers- Arcania is here."

And it has the yellow exclamation mark, as someone already pointed out.

So Arcania seems very likely. Hopefully, this doesn't mean that there won't be any classic release at all next week.

I hope it's somehow a hint for Risen 1+2, though I can't possibly make a connection to the games and the hint, other then the hint seems to suggest an RPG.

I'll go with Wizardry 1-5, for lack of a better idea.

Black and White?

I know I am probably (obviously) wrong, but it had fetch quests and there were plenty of little people with exclmation marks.

Reading the description of the video:

Yup, that's another one of those clever Enigmatic T hints for a game soon to debut on GOG.com!

The word debut caught my eye.
That would indicate something brand new, first time released.

Still no clue what it is but thought I'd throw that in for the smarter people here. :)

https://www.youtube.com/watch?v=wwaMm_lW59Q

So when will GOG release Night Trap or DreamWeb ?

Sacred 2 also has exclamation marks

There are various fetch side quests in the Torchlight games. I actually missed one of the items you're supposed to fetch and proceeded on without realizing it was important, causing the game to be unfinishable because I was unable to go back and retrieve the item a second time and it vanished. Had to start the game over again (Torchlight 1).

It just occurred to me that everyone seems to be trying to think of a game that came on 5 CDs which is an RPG, however... it could be a game that came on 5 DVDs and be 20+GB. Sure, it's less likely but anything is possible and we do have games that are larger than that in the catalogue already, including RPGs. I've no idea what to throw out there as a guess though as anything I might have guessed is pretty much already on GOG. :) I guess I'll throw "Torchlight 2" out there with others that suggested that.

(Even though Torchlight 2 isn't a 5 disk game ... )