For me that'd be:
Planescape: Torment
Grim Fandango
The Cat Lady
Deadly Premonition
Sanitarium (or Fallont 2...)

Where's Alan Turing? Ellen DeGeneres? Harvey Milk? George Takei?

1) Witcher series.
2) Diablo series up and until 2 LOD.
3) Vampire the Masquerade series.
4) Command and Conquer series, up and until The First Decade.
5) GTA 5.

Maybe not in this order. And if they would be allowed to be 10...

6) Sid Meiers Pirates 2004.
7) Baldur's Gate series.
8) The Suffering series.
9) Shadow Warrior Remake.
10) Aion.

In not particular order and without thinking too much:

Master of Orion 2
Advance Wars 2
Civilization 5 (I never was able to get into the previous ones but I think I'll give them another chance.)
Duke Nukem 3D
Half Life

In no particular ordering within "top 5", and for various reasons:
Deus Ex
Diablo 2
Final Fantasy Tactics
Civilization 4
Super Mario World

Expanding to ten (clearly ordered as "less than top 5", but not within each other):
Pirates! (Either version)
Final Fantasy 6 or 10 (impossible to select one over the other; one has narrative; other has game play)
RollerCoaster Tycoon (pick one; I pick say 3)
Zelda 3 A Link to the Past
Super Metroid

Okay, five console games above. Here are PC replacements:
Warcraft 3
Unreal Tournament (original)
The Sims 3
Dungeon Keeper
SimCity 4

Underrated honorable mention:
Armies of Exigo

1. UFO: Enemy Unknown
2. Beyond: Two Souls
3. Dragon Age: Inquisition
4. Uncharted 2: Among Thieves
5. Elder Scrolls III: Morrowind

In no particular order (all of these are legendary in their own right)
---------------------
Tyrian 2000

Most detailed game of its type, with the most options, secrets, difficulty choices, etc. Also features a unique "loopback" where once you finish the last level, the game loops back to the first one instead of ending. Last time I checked, Tyrian 2000 is either public domain or open source, and it's freely available on GOG. Go play it now - if you have time and haven't played it, you have no excuse not to.

Newer games of the same type have better graphics, but as far as actual customization and strategic depth are concerned, none of the newer games have anywhere near as much.
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Inner Space

If anyone else has played it or even heard of it, I would be surprised. It's supposedly the only games that has been played in the same way from the original Windows 3.x until today.

Wide variety of spaceships and items. Randomly generated waves/missions. Incredible detail and visual effects for its time. Amazing considering it was written in the early 1990's.
-----------------
Might and Magic VII

The pinnacle of a legendary series, probably better than the rest of the series combined. Single-player, multi-character real time combat, with a turn-based option. Superior game design, balancing, variety of NPCs. Original storyline with 2 paths for replayability. I also challenge you to find any game that makes 640x480 2D sprites look more detailed. As far as I know, there are no other games made in its style besides Might and Magic 6 and 8.
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Elder Scrolls IV: Oblivion

A lot of you are probably going to question why I didn't pick Morrowind (best storyline in an Elder Scrolls game) or Skyrim (for the better game engine). The main reason is that Elder Scrolls IV: Oblivion was the last game in the series with a disc-only option for PC, and it actually had a functional scripting engine unlike Morrowind. (Skyrim is only available on Steam for PC games. Moral of the story for developers/publishers: mandatory DRM and discrimination against PC gamers = miss out on awards)

NOTE: If you are planning on getting the disc edition of Elder Scrolls Oblivion, avoid the "Game of the Year" edition (specifically, avoid the Shivering Isle expansion) - I read somewhere that it comes with some DRMs that can damage your computer. As far as I know, the base game has only a disc check as DRM (must have the disc in a DVD reader to run the game).
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Jazz Jackrabbit

Combat-oriented platformer - unlike most other platformers that attempted to imitate Nintendo's Mario franchise, Jazz Jackrabbit was about fighting turtles instead of difficult jumps and maneuvers. It also had a sequel that supported splitscreen multiplayer.

In no particular order:

- Civlization 2
- Neverwinter Night 1
- Tetris
- Vampire the Masquerade: Bloodlines
- Sid Meier's Alpha Centauri

And runners-up:

- Call to Power 2
- Heroes of Might and Magic 2 and 3
- Baldur's Gate series
- Icewind Dale series
- Europa Universalis IV
- Divinity Original Sin
- Wasteland 2

Best multiplayer game:

- Neverwinter Night 1

Going off the top of my head and going by "favorite" rather than "best" (which would probably look quite different), in no particular order-

King's Quest V/Space Quest III
Master of Orion
Commander Keen 4
Command and Conquer (Red Alert 2 if I have to pick just one)
Star Wars Battlefront 2
Tie Fighter/X-Wing
Star Trek 25th Anniversary
LotR: Return of the King
Battle for Middle Earth
Madden
Medal of Honor Allied Assault

A lot of these get the nod for nostalgic value. Twenty games is about as low as I could honestly narrow my list down to, but I figured I was stretching "top 5" as it was.

5 is hard to pick.

PC:
Deus Ex
Planescape Torment
Fallout 2
Leisure Suit Larry 7
Fallout 3 / New Vegas

Console:
Zelda: A Link to the Past
Super Metroid
Castlevanis: SOTN
Final Fantasy VII
Super Mario World

Well I had bought Baldur Gate series 9 times

4 physical copies, one on Impulse / Gamestop, one on Gamer Gate, one on steam, one on GOG and another enhance edition on GOG.

Maybe I will get the I pad version of BG if I ever buy an I pad

For me, the bst games of all time are:

1. Tomb Raider
2. Omikron: the Nomad Soul
3. Resident Evil and Silent Hill (couldn't pick just one)
4. Final Fantasy VII
5. The Legend Of Zelda: Ocarina of Time

Honourable mention: Persona 3

We must be the same generation. It's nice to meet someone in here my age but the trip down memory lane is a scary one! :P

I thought everyone here was old at heart. There's a twentysomething ^ up above telling people to get off her lawn. 90 is older. Fear 90, especially when that 90 year old has better teeth and eyes than young strong children.