If you could only play one game for each letter of the alphabet...

[Johnny Novgorod]

A - Age of Empires 2
B - (The) Binding of Isaac: Rebirth
C - Crusader Kings II
D - Dynasty Warriors 8: Extreme Legends Complete Edition
E - Empire Earth
F - Flatout: Ultimate Carnage
G - Galactic Civilizations II
H - Heroes of Might and Magic 5
I - IL-2 Sturmovik: 1946
J - Just Cause 2
K - Kerbal Space Program
L - Little Big Planet 2
M - Mount & Blade: Warband
N - Nuclear Throne
O - Okami
P - Painkiller
Q - Quake Live
R - Rise of Legends
S - S.T.A.K.E.R.: Shadow of Chernobyl
T - Titan Quest
U - Unreal Tournament 2k4
V - Vampire: The Masquerade - Bloodlines
W - War Thunder
X - X3: Terran Conflict
Y - Yoshi's Story
Z - Zone of the Enders: 2nd Runner

There you go. Not necessarily 100% since I probably forgot about some obvious better choices, but it will do.

 

[Varrdy]

Oooh! A timewaster - I'm in!

I have only gone with games I have played so there's a real mixed-bag of old and not so old. The only one I failed at was "Y" - I just couldn't find a game whose title starts with a "Y" and I have played.

A) Ace Combat 6: Fires of Liberation
B) Bubble Bobble
C) Cannon Fodder
D) Driver: San Francisco
E) Elder Scrolls V: Skyrim, The
F) Fallout: New Vegas
G) GTA 5
H) Halo
I) Ivan "Ironman" Stuart's Super Off-road Racer
J) Jungle Strike
K) Kerbal Space Program
L) Lemmings
M) Mass Effect
N) Nomad
O) Outrun
P) Psycho Pinball (if only for the awesome music!)
Q) Quake: Painkeep
R) Red Dead Redemption
S) Sonic the Hedgehog 2
T) Terminal Velocity
U) Urban Strike
V) Virtua Fighter
W) WWE 13
X) XCOM: UFO - Enemy Unknown (original MS DOS version)
Y)
Z) Zoo Tycoon

 

[aozgolo]

This looks fun but some letters are gonna kill me I just know!:

A) Assassin's Creed Black Flag
B) Baldur's Gate II Enhanced Edition
C) Chrono Trigger
D) Dragon Quest VIII
E) Earthbound (Mother 2)
F) Fallout New Vegas
G) Gnomoria
H) Harvest Moon: Magical Melody
I) Icewind Dale Enhanced Edition
J) Just Cause 2
K) Kingdoms of Amalur: The Reckoning
L) Legend of Mana
M) Mount & Blade Warband
N) Nox
O) Oddworld: Abe's Exoddus
P) Psychonauts
Q) Quest for Infamy
R) Red Dead Redemption
S) Skyrim (yeah I cheated)
T) Terraria
U) Ultima VII
V) Valkyria Chronicles
W) Witcher 2
X) XCOM Enemy Unknown
Y) Ys Chronciles
Z) Zombies ate my neighbours

Soooo many games I had to leave off...

Letters I now hate:

B (Banished, Beyond Good and Evil, Brutal Legend, Bully)
D (Don't Starve, Dragon Quest IX, Dragon Age Origins, Don't Starve)
F (Fable TLC, Final Fantasy XII, Fallout 2)
G (GTA:5, Golden Axe III)
M (Mass Effect 2, Morrowind, Minecraft)
S (Suikoden II, Super Mario RPG, Secret of Mana, Secret of Evermore, Shadow of Colossus, Simcity 4)

 

[Mimic]

A - Aliens vs Predator 2
B - Batman: Arkham Asylum
C - Chronicles of Riddick: Escape from Butcher Bay
D - Dragon Age: Origins
E - Extreme G
F - Fallout 3 FEAR, Fire Emblem: Sacred Stones
G - Goldeneye
H - Human Revolution (Deus Ex)
I - ICO and Shadow of Colossus Collection
J - Journey (had a hard time picking this over Jet Force Gemini)
K - ...
L - Last of Us, The
M - Might and Magic: Clash of Heroes
N - Need for Speed Hot Pursuit
O - Ocarina of Time (The Legend of Zelda)
P - Portal 2
Q - ...
R - Red Dead Redemption
S - Super Mario galaxy
T - To the Moon
U - Unreal Tournament 2004
V - Valiant Hearts
W - Witch's House, the
X - Xenoblade Chronicles
Y - ...
Z - ...

 

[Evonisia]

What do expansion packs count as? Using Halo 3: ODST as an example, it's technically an expansion pack to Halo 3 but is very much a game of its own in terms of content, so would saying Halo 3 count as being able to have both it and ODST?

Just like how if you chose WoW you could stay in TBC forever or something like that.

 

[Vigormortis]

Hmm....interesting challenge. I'll give it a go...

A: Alan Wake
B: Banjo Kazooie
C: Conker's Bad Fur Day
D: Diablo 2
E: Earth: Above and Beyond
F: Freespace
G: Garry's Mod
H: Half-Life
I: Ikaruga
J: Jet Force Gemini
K: Killing Floor
L: Lemmings
M: Metroid Prime
N: NetStorm
O: Outlast
P: Portal 2
Q: Quake 3: Arena
R: Rogue Squadron
S: Sins of a Solar Empire: Rebellion
T: Terraria
U: Uru: Ages Beyond Myst
V: Viewtiful Joe
W: Wetrix
X: Xtreme G 3
Y: Yoshi's Island
Z: Zork: The Grand Inquisitor

Upon attempting this list, I came to realize there are a LOT of games I could put in the H, M, and S categories...

 

[Sixcess]

A - Amnesia The Dark Descent
B - Bushido Blade
C - Civilisation II
D - Doom
E -
F - Fear Effect
G -
H - Halo: Combat Evolved
I -
J - just Cause 2
K - Kerbal Space Program
L - The Lord of the Rings Online
M - Minecraft
N -
0 - Oddworld: Abe's Oddysee
P - Postal 2
Q - Quake
R - Ryzom
S - The Secret World
T - Tenchu
U - The Urbz
V - Velvet Assassin
W - World of Warcraft
X - XCOM Enemy Within
Y -
Z -

Choosing Fear Effect over Fear Effect 2 or Fallen Earth was my hardest pick.

And an honourable mention to Hooligans: Storm Over Europe, which almost took H before I remembered Halo.

 

[PolarBearClub]

A) Arkham Asylum (cheating already?)
B) Bioshock
C) Castlevania 2: Lord of Shadow (I wanted to say Advanced Warfare, mainly because it's a CoD title I'm actually good at, but I'm considering this a 'play for the rest of your life' situation)
D) Dragon Age: Inquisition
E) ....Enslaved?
F) Final Fantasy X
G) GTA V
H) Harvest Moon
I) ICO
J) Just Cause 2
K) Knights of the Old Republic
L) Last Remnant
M) Metal Gear Solid (first one for the PS1)
N) NBA Jam (sega version)
O) Ocarina of Time
P) Pokemon X
Q) Quake III
R) Red Dead Redemption
S) Super Mario 3D Land
T) The Elder Scrolls: Skyrim
U) Ultimate Marvel vs Capcom 3 (never played it, we're into the realms of the tougher letters here. Only fighting game on the list, good to have variety)
V) Viva Pinata (Xbox 360)
W) Witcher 2
X) X-com: Enemy Unknown
Y) Ys I & II Chronicles
Z) Zelda: Majora's Mask

Lots of RPGs and action/adventure games. A good few of them are well over 20-30 hours playing time too. Enough to keep me happy.

 

[Squilookle]

A) Assassin's Creed II
B) Battlefield 1942
C) Crimson Skies
D) Driver
E) Endless Ocean: Blue World
F) FarCry 3
G) Goldeneye 007
H) Hotline Miami
I) Interstate 76
J) Just Cause 2
K) Kerbal Space Program
L) Left 4 Dead
M) Mercenaries
N) Noone Lives Forever
O) Operation Flashpoint: Cold War Crisis
P) Perfect Dark
Q) Quake III
R) Re-Volt
S) Sim City 2000
T) TIE Fighter
U) Unreal Tournament 2004
V) Vice City
W) Warband
X) XCOM: Enemy Unknown
Y) Yoshi's Story?
Z) Zoop

 

[RedDeadFred]

A -Assassin's Creed IV
B -Borderlands 2
C- Civilization V
D -Dishonored
E -Elder Scrolls V, Skyrim
F -Fallout 3
G -Guild Wars 2
H -Hotline Miami
I -Injustice
J -Just Cause 2
K -Killing Floor
L -Legend of Zelda: The Wind Waker
M -Mount and Blade Warband
N -No More Heroes 2
O -One Finger Death Punch
P -Portal
Q -Quake III
R -Rock Band 2
S -Shadow of Mordor
T -Torchlight II
U -Unreal Tournament
V -Vanquish
W -Witcher 2
X -XCOM: Enemy Unknown
Y -Yoshi's Island
Z- Ziggurat

I have not played all of these games, but I think I'd enjoy the ones that I chose to fill the letters I was unsure about.

 

[LaoJim]

A) Akai Katana
B) Bayonetta (haven't played 2 yet)
C) Civilization 4
D) Diddy Kong Racing
E) Elder Scrolls 5: Skyrim
F) Forza 4
G) Geometry Wars 3
H) Hobbit (1980s text adventure)
I) IL Sturmovik
J) Jet Set Willy
K) Kingdoms of Amalur
L) Lego Star Wars
M) Marvel vs Capcom 3
N) Need for Speed Underground 2
O) Orange Box
P) Plants vs Zombies
Q) Quake
R) Rayman Origins
S) Sleeping Dogs
T) Tetris
U) Ultra Street Fighter 4
V) Viva Pinata
W) Witcher 2
X) XCOM
Y) Your Shape Fitness 2012
Z) Zumba Fitness

 

[Gashad]

Went with the game I enjoyed playing the most when it was released for each spot(a couple of spots the game was the only one I had played starting with that letter).

A) Arcanum
B) Baldurs gate 2
C) Civilization V
D) Dota( the most hotly contested spot with both dragon age and Diablo II contesting)
E) Europa Universalis 4
F) Faster Than Light
G) GTA 2
H) Heroes of Might and Magic III
I) Icewind Dale
J) Jade empire
K) Knights of the old republic II
L) Left for dead II
M) Mass effect 2
N) Neverwinter Nights 2 Mask of the Betrayer
O) Orcs must die II
P) Payday II
Q)
R)Resident Evil IV
S) Star Craft 2
T) Tomb Raider(2013)
U) Unreal Tornament 2004
V) Vampire: The Masquerade: Bloodlines
W) Witcher 2
X)
Y)
Z)

 

[DarkhoIlow]

A: Arcanum
B: Baldur's Gate II
C: Castlevania Lords of Shadow
D: Dragon Age Origins
E: Elder Scrolls III: Morrowind
F: Final Fantasy VII
G: Gothic II
H: Half Life 2
I: Icewind Dale
J: Jade Empire
K: Knights of the Old Republic II
L: Last Story, the
M: Mass Effect 2
N: Neverwinter Nights
O: Okami
P: Planescape Torment
R: Resident Evil 4
S: Starcraft II
T: Titanfall
U: Unreal Tournament
V: Vampire the Masquerade: Bloodlines
W: Witcher 3, the (4 months away but it still counts! fallback is Witcher 2, the)
X: Xenoblade Chronicles
Y: Y's Chronicles
Z: Zeno Clash

Very interesting idea, kudos sir!

 

[legend of duty]

A. Amped 3
B. Bully: Scholarship Edition
C. Call of Duty: World at War
D.
E.
F. Fallout: New Vegas
G. Grand Theft Auto 5
H. Halo Reach
I.
J. Jak and Daxter
K.
L. Left for Dead 2
M. Mario Galaxy
N.
O. Orange Box
P. Punch Out Wii
Q.
R. Resident Evil 5
S. Sonic ultimate genesis collection
T. Tropico 4
U.
V.
W.
X. X-Men arcade game
Y. Yoshis's Story
Z.

 

[Wintermute_v1legacy]

A) Ass Creed Ezio Collection
B) Bastion
C) Commandos 2 Men of Courage
D) Diablo II
E) Skyrim
F) Far Cry 3
G) GTA (the very first one)
H) Half-Life 3
I) Invisible, Inc
J) ...
K) Killzone Trilogy Collection
L) LA Noire
M) Mass Effect Trilogy Collection
N) No One Lives Forever
O) ...
P) Papers, Please
Q) Quake III Arena
R) Red Dead Redemption
S) Sleeping Dogs
T) Tomb Raider 2013
U) Ultra Street Fighter IV
V) ...
W) The Walking Dead
X) ...
Y) ...
Z) ...

 

[DFDelta]

A) Aurora 4x
B) Bubble Bobble
C) Chrono Trigger
D) Dwarf Fortress
E) Elona (stop looking at me like that)
F) Fatal Frame III
G) Garry's Mod
H) Hearthstone
I) Illusion of Time
J) Joust
K) Kerbal Space Program
L) Legend of Kyrandia II: The hand of fate
M) MechWarrior: Living Legends
N) NetHack
O) Omikron: The Nomad Soul
P) Phantasy Star Online
Q) Quake III Arena
R) RimWorld
S) Star Citizen (if it turns out the way it seems to be)
T) Touhou 12: Undefined Fantastic Object (they are all good, but this one has the best music)
U) Unreal Tournament
V) Vindictus
W) Warframe
X) X3: Albion Prelude
Y) Ys Origin (all of them are good, but if I have to pick one then Origin it is)
Z) Zone of the Enders II

 

[pearcinator]

A) Amnesia: The Dark Descent
B) Banjo-Tooie
C) Curse of Monkey Island
D) Dragon Age: Origins
E) Elder Scrolls: Skyrim
F) Fable: The Lost Chapters
G) Goldeneye 007
H) Halo: Masterchief Collection
I) Indiana Jones and the Fate of Atlantis
J) Jade Empire
K) Knights of the Old Republic
L) Legend of Zelda: Majoras Mask
M) Mass Effect 2
N) No Man's Sky (if that counts)
O) Oddworld series
P) Portal 2
Q) Quantum Conundrum
R) Runescape
S) Super Mario 64
T) Team Fortress 2
U) Uncharted 3
V) Vampire: The Masquerade Bloodlines
W) Witcher 3: Wild Hunt
X) Xenoblade Chronicles X
Y) You Don't Know Jack series
Z) Zelda: Ocarina of Time

Some of these games I haven't even played (or even released yet haha). I don't know if you can count them but oh well.