Glad I'm not alone...

I would imagine that the unexcelled refers specifically to something they're bringing to GOG. So either the publisher themselves (financially unexcelled) or the rating of one of their games that will actually be here on Thursday.

I see "<!-- grande spot finito -->" in the source....
Maybe GOG is getting Taco Bell??.

Splinter Cell :-)
Expect the unexcelled
un - not
ex - out
So something would also be thinkable that plays in a cell. Cell -> Prison -> hmm...?

I'm sorry but Splinter Cell is not that great to warrant its own countdown. Besides, we already have Ubisoft here...

It's so, so easy when you have the answer :p

Yeah, I know, I'm just throwing rocks at the water to see which ones float :-P

Stop the countdown. I found it. You talk too much Mikee. Way too much.

Actually the big secret is that on Thursday the GOG homepage will re-direct here

You're a master of deduction, Cambrey.

So it's NOT Max Payne D: ?!

All the games and publishers mentioned that according to the clue 'one of them is correct'.
There are a lot in the list that wouldnt warrant a countdown timer.
System Shock 2
Wing Commander
Ultima
Deus Ex
Warcraft: Orcs and Humans
Lost Vikings
Blackthorne
Resident Evil
Megaman
interstate '76
IW
LOOM
Leisure Suit Larry
Space Quest
Tomb Raider
Thief
Team 17
MSX
Grim Fandango
Full Throtle
Day Of The Tentacle
Final Fantasy
Theme Hospital
Theme Park
Syndicate Wars
Sid Meier's Alpha Centauri
Dungeon Keeper
Populous
C&C
Desert Strike (and sequels)
Sim City 2000
Sim stuff
Ultima Collection
System Shock
Total War
Big Rigs: Over the Road Racing
Hitman
X-Com
Zork
Planescape
MS Excel
Baldur's Gate I and II
The Bard's Tale
Icewind Dale I & II
Dungeon Keeper
Age of Empires
AoE II
Monster Truck Madness 2
Midtown Madness 2
Motocross Madness 2
Homeworld
Master Of Orion
DAIKATANA
Rise of Nations
Mechwarrior
Halo
ELITE
X-Wing
Desert Strike
Outlaws
Yoda Stories
Tribes
YDKJ
NASCAR Racing games
Grand Prix Legends
WORMS
Starcraft
Diablo
Duke Nukem Forever
FEAR
Monkey Island
Caesar II-III
Master of Olympus
Master of Atlantis
Pharaoh
Cleopatra
WIZARDRY
Harvester
11th Hour
Shivers 1-2
Phantasmagoria
Clive Barker's Undying
American McGee's Alice
id software
LucasArts
Activision
Blizzard
CAPCOM
Sierra
Eidos
EA
Origin
Microprose
Bullfrog
Atari
Rockstar
BioWare
THQ
Sega
Westwood
Maxis

Apparently not T2 either. So back to puzzling back hints...
Unexcelled = Not capable of being improved on = Final
Back to Square Enix? ;)

What is unexcelled? Something that has not ascended more. The word comes from Latin excel. Exceksior!
And what is an excelsior? An ascension!
So Origin Systems (Ultima 9: Ascension!) is a guess.
However, what would really be unexcelled?
Selling new games and not only old ones for low prices? A huge step forward for games if they become DRM-free again.
Selling games developed on their own? Not really, they don't have enough time for that.
Getting ESA games for the catalogue? Would be a big deal.
No, something that never has been done before would be to sell console games for PC! Legal possibilities of owning commercial ROMs and play the real good old games for PC! This would be something that never has happened before and would really fit to the website since many of those are really good old games. Final Fantasy VII (which incidentally is also available for PC) still counts as the best game of all time, story-wise at least.
Unexcelled however also could be a pun against MS Excel as has been said before. So the Microsoft games maybe? Age of Empires for example? Great but would not justify a countdown.
Well, if it really is the biggest thing since the launch of the website, it will be something worth waiting the few days for. But please let it not be selling movies or such. :-)