Difficult one... I guess:

Singleplayer:

1: Halo (franchise)
2: Half-Life 2 (+ episodes)
3: God of War (franchise)
4: Escape from Butcher Bay
5: Knights of the Old republic (1 & 2)
6: Dead Space (franchise)
7: Splinter Cell (1, 2 and 3)

Multiplayer:

1: Halo 3
2: Gears of War
3: GRID
4: Command & Conquer
5: Nothing specific springs to mind right now...

I'm only doing it for this gen

Single

1. Fallout 3
2. Gran Turismo 5
3. Uncharted series (If I need to be more specific, I'd pick Drake's Fortune)
4. Oblivion
5. Rainbow Six Vegas (including co-op stuff like Terrorist hunt)

Multi

1. Call of Duty 4 (the only online focused game I can think of that stayed more popular than it's successor)
2. Halo 3
3. Rainbow Six: Vegas
4. Resistance Fall of Man
5. Black Ops

Single:

1 - Xenoblade Chronicles
2 - Lost Odyssey
3 - Dark Souls
4 - Fatal Frame 4
5 - Metroid Prime Trilogy

Multi:

1 - Monster Hunter 3tri
2 - Mario Kart Wii
3 - Call of Duty Black Ops
4 - Mario Tennis Open
5 - Dark Souls

Off the top of my head

Single player

Skyrim
Red dead redemption
Majora's Mask
Mario 64
Final fantasy XII

Multiplayer

Call of duty Black ops
Halo 3
Mario kart 64
World of Warcraft
Smash bros brawl

When it comes to single player its nothing great but the Multi player is argubaly the best in gaming history. It's like Halo + Uncharted + Warhawk. 

I loved your overall post I think I should include that in my OP! Thanks :)

I said that around 6 months ago. Anyways GTA IV, Red Dead Redemption and Uncharted 3 are my favourite games. It depends on my mood which one I prefer.

Single player:

1.) Uncharted 2

2.) FF VIII

3.) Legacy of Kain: Soul Reaver

4.) Legacy of Kain: Soul Reaver 2

5.) Batman: AA

Multi Player:

1.) America's Army Operations

2.) Age of Empires 2 (with expansions)

3.) Tom Clancy's Rainbow Six: Rogue Spear (with expansions)

4.) Battlefield 3

5.) Killzone 3

Single Player:

1) Final Fantasy VII
2) Demon's/Dark Souls
3) Panzer Dragon Saga
4) Ico
5) Anno 1404

Multi Player:

1) Rock Band 1-3
2) Dota
3) Counter Strike 1.0-1.6 (before it got infested by hackers)
4) Dance Dance Revolution
5) Motorstorm 1 (very rough, but also really fun) / Hot Shots Golf 5 (sadly pretty empty, but superb system and so mature people) <- can't really decide between those 2

Single player:
1.) Chrono Trigger (SNES)
2.) Super Mario RPG (SNES)
3.) Super Mario 64 (N64)
4.) Zelda Ocarina of Time (N64)
5.) Conker's Bad Fur Day (N64)

Multi Player:
1.) Mario Kart 64 (N64)
2.) Perfect Dark 64 (N64)
3.) Golden Eye (N64)
4.) Conker's Bad Fur Day (N64)
5.) Mario Kart Wii (Wii)

Mario Party 1 (N64), Wii Party (Wii), Counter Strike (PC), Street of Rage 2, Street Fighter 2, Ninja Gaiden (NES), Mega Man (NES), Super Mario Bros 3, so many games to put in a tiny list.