Doesn't really change anything, since the more recent AAA-ish titles (AKA the games currently offered in the Big Games sale) are still absent.

As of recently, is everyone is more or less drawing from the exact same pool of games, with maybe one unique game per bundle?

Maybe I should rank them like loot drops in RPGs - Common, Rare, Elite. :)

Conclusions from 50 test rolls:
Note: I have not purchased any Pots of Gold. Results may be wildly different for people who have purchased previous pots.

If you own a game it will not appear in a roll.
Games are randomly drawn. However, games marked as wanted on the wishlist have a FAR greater chance of appearing in a roll (close to 100% chance if the game is on the list below).

These games are what is randomly drawn from:
Alien Shooter
Alien Shooter 2
Aqua Kitty: Milk Mine Defender
Avernum: The Complete Saga
Duke Nukem 3D Atomic Edition
Geneforge 1-5
Giana Sisters: Rise of the Owlverlord
I Have No Mouth And I Must Scream
Ittle Dew
Painkiller Black Edition
Penumbra Collection, The
Puddle
System Shock 2
Tales from Space Mutant Blobs Attack
Zombie Shooter
Zombie Shooter 2

These games are either extremely rare or no longer offered (have not seen in 50 blank rolls):
Aarklash Legacy
Amnesia: A Machine for Pigs
Cognition: An Erica Reed Thriller
Deadly Premonition
Deponia 3 Goodbye Deponia
Memoria
Outlast (I've seen it once in 50 rolls)

The games in the pool from the big sale would need a special category like "Diablo 3 v1.0 Legendary".

Though I think the BIG games are neither Rare, Elite or Legendary - it's just plain impossible to get them now.

EDIT: You could call the category "(Probably) impossible to get".

Thanks for the analysis, Melhelix! Very useful.

It confirms I was right to grab Deadly Premonition when it rolled around for me, even though it was for gifting.

I suspect you may be correct. Perhaps GOG programmed in a set amount of these titles to be given away, with a diminishing chance against the remaining pool. So while they might have shown up in every 20 bundles when there were a 1000 of them, they might only show in every 10,000 once there are just 5 left.

This is pure speculation, but they do seem to be harder to obtain than at the debut.

I've rolled about 20 times, and Ittle Dew has been in 90% of the rolls. Same with Puddle. Usually they're both present. Of the games in the most recent list, I only own Avernum, Geneforge, and System Shock 2 so it's weird that Ittle Dew / Puddle are basically guaranteed rolls. I think they must have a very high chance of appearing.

I haven't seen a single "Shooter" game (Alien or Zombie).

I Have No Mouth And I Must Scream has shown up 100% of the time; it's in my wishlist.

I think I can now also confirm that the system takes into account either how many Pots you already bought (my guess), or how many of the possible games you already have (more unlikely, I think).

With this account (8 Pots) I alway get Alien Shooter, Zombie Shooter, Zombie Shooter 2 plus two games I already own (which includes Alien Shooter 2).

With the new test account I have never seen any of these games.

I think I had more fun rolling than actually playing games I own. :P

I'm really kicking myself for not grabbing a roll with Aarklash last night. But I have a rule, no purchases between 11 pm - 6 am. It's saved me from making some really silly decisions, heh.

I am very glad they ran the 90% off sale and the 75% off sale concurrently. Makes for a solid mix. I'll be curious to see if the balance shifts again on Monday, ie. if they add new games to the pool.

I've tried several times now to pick 3 games and get two pots of gold that I like (using the CTRL-U and search for 'data-title' trick in Firefox), but the only pot that I like so far is Puddle. It gets some bad reviews, but I like the idea of a simple to control game that's physics based. But alas as final game, I keep on getting one of these:

Avernum,
Aqua Kitty
Ittle Dew,
Penumbra
and lots and lots and lots of Painkiller draws. And though the game looks nice, the heavy-metal soundtrack drives me crazy (and I'm crazy enough of my own as I am).

Is there a way to Proceed the order with gifting one I don't like?

Gift the whole order to your own email address, then give the code for the game you don't want to someone else?

I noticed that GOG generates a specific URL for a specific set of games, and I can enter these links and return to a previous roll. They also work cross browser, but it has me log in, so I wonder if these URLs are tied to specific accounts. Someone give this a shot and see if it gives the same games:

https://secure.gog.com/checkout/5sta5qu4dpx

Duke Nukem 3D
Zombie Shooter 2
Alien Shooter
Mutant Blobs Attack
Puddle

Only if you already own the game on GOG. Gift codes on GOG are one per purchase. Thus a gift code for a purchase of five games has all five games on it. All games are redeemed automatically at the same time when the code is used. The only exception is if a person already owns a copy of the game. Then that game stays on the gift code and everything not already owned is redeemed.
Looks like it's account tied, for me it's a 404.