my favourite game (even if probably it's not the best i've played) is Postal 2

Chrono Trigger. The gameplay, the replayability, the story, and the fact that involves time travel. Everything about the game is amazing!

Planescape Torment. Excellent writing is sadly still a rarity in video games 11 years later. Also because of it I just can't enjoy games with badly written dialouge anymore. Thankfully thats not too often the case.

Batman: Arkham Asylum, Assassin's Creed 2 and Warhammer rts games.

Planescape: Torment (All time favourite! Take us back to the good old days of WRPGs!!!)
Honourable mentions go to:
Baldurs' Gate 1 & 2
Fallout 1 & 2
Jagged Alliance 2
Red Dead Redemption (loved the story/characters if the game did get a bit repetitive)

Final Fantasy 6 (3 in the US, All time favourite JRPG!!!)
Honourable mentions:
Suikoden 1 & 2 (never played 3, so sad)
Breath of Fire 4
Xenogear
Final Fantasy 7 & 8

Yeah i"m an RPG nut... but i find that I don't have as much time to invest in those games today...

I have played AOE and AOM. they are good games. good story.

And also i like

Heroes of Might and Magic IV
Final Fantasy VIII
Final Fantasy IX
Final Fantasy X
The legend of the dragoon.
Chrono Cross
The dungeon siege 2 (PC)

In action games,
i like COD MW1 , COD MW2 , COD Black ops, Medal of Honour. Prince of Persia: the sand of time. Assassin Creed. Metal Gear Solid 2

Iphone game.
Angry Bird, Cut the rope.

FF X is the best though. don't like the FF X-2

I would have to go with either a Metal Gear game or a Suikoden game.

Ok I generally try and avoid jumping in to threads like this but every has checked their macho shit and the door so I'll through my choices in the ring.
As others have said I think it's only fair the following games get some love in no particular order.
Age of Empires 1-3, Mythology
Thief : The Dark Project.
Duke Nukem 3d ( Oh how I miss the old DOS loading screens)
Desert Strike : Return to the Gulf on the Sega MD
Delta Force : Land Warrior on PC, played it literally to Death.
GTA Vice CIty
Metal Gear Solid 1-3
Resident Evil 4
Final Fantasy X
Mass effect 1-2
KOTOR 1-2
Elder Scrolls : Morrwind ( Just couldn't get in to Oblivion)
Fallout series (I am obsessed with it's world, I love it)

Now my selection for the greatest game ever and it's an odd choice so I hope a few of you have played it/them:
Zork : Nemesis on PC, that game kicked my ass as a kid, I couldn't even guess at how long it took me to complete.
And then number one, Zork : Grand Inquisitor. Now these are just point and click puzzle rpg's but my god they made me so happy. As recently as last year when I got a bad flu, I found my copy of ZGI and played through it for maybe the 6th time.
It made me fall in love with games even more intensely than I thought possible. Plus Face from the A-Team is in it! Ah memories.....

GOW,FF7,8,10 and zelda franchise and metal gear solid franchise.

These are my fave

Knights of the Old Republic
Shenmue
Mass Effect series

Most of these I have played apart from World of Warcraft out of fear of loosing my normal "working" life

My favourite game is Edna and Harvey: The Breakout!
Its a sooo genius and funny comic-adventure here from germany!

My favorite has to be Castlevania: Symphony of the Night. I've replayed it about 10 times and probably will another 10.

nightcrawlers

Personally I think a lot of the time people quote their favourite game of all time based on the memories of playing that game, or associate with a certain period of their life. It can sometimes be disappointing to revisit and play some of those games that you thought were great.

A few of my faves listed here are ones I still go back and play even now.

Secret of Mana
Diablo 2
Half life 2
Final fantasy VII
Chrono trigger
Resident Evil 4
Smash TV
Bubble Bobble