20 is a lot but if I think off the top of my head (definitely not in order):

Titan Quest + Immortal Throne
Overlord 1
Return to Castle Wolfenstein
Doom 1+2
Blood
Age of Empires 2
Red Alert 2
Disciples II
HoM&M III
HoM&M V
Serious Sam series (only the main games and excluding 2 (until the remake at least))
Worms Armageddon
Medal of Honor: Allied Assault
Unreal (Tournament) series
LOTR: The Battle for Middle-Earth 1
Age of Mythology
Indiana Jones and the Infernal Machine
Die by the Sword
Rune
Drakan: Order of the Flame

1 Speedball 2 - Amiga
2 Baldurs Gate 2 - PC
3 Divinity: Original Sin 1/2 - PC
4 Turrican 2 - Amiga
5 Civilisation 5 - PC
6 Diablo 2 - PC
7 The Settlers - Amiga
8 Back to Skool - Spectrum
9 Half Life 2 - PC
10 Sensible World Of Soccer - Amiga
11 Fallout 2 - PC
12 Rainbow Islands - Amiga
13 Pinball Fantasies - Amiga
14 Berks 3 - C16 Plus/4
15 Ultima Online - PC
16 Blade Runner - PC
17 Hired Guns - Amiga
18 Target Renegade - Spectrum
19 Morrowind - PC
20 Lemmings - Amiga

What's wrong with SS2? Honest question, I've never played it.

Dragon Age
Elder Scrolls - Oblivion & Skyrim
Witcher 1 & 2 ( PC not good enough for 3)
Two Worlds 1 & 2
Gothic Series ( 1-3)

Broken Sword Series
Gabriel Knight Series
Syberia
The Longest Journey
Stardew Valley
And most of Frogwares games:)

How is the remaster or have you not tried it?

It is more of a joke game and has such a terrible plot right from the beginning, making everything from First and Second encounter absolutely irrelevant, that even Croteam proclaimed it non-canon.

Imagine wacky and then multiply it by a million. You might get close to what SS2 is. The changed design style also does not help at all (Sam barely even looks like himself). The whole game is like "what if Sam had a trippy dream".

Star Wars: Knights of the Old Republic II - The Sith Lords
Mount & Blade: Warband
Dark Souls: Prepare to Die Edition
Mass Effect 2
The Witcher 3: Wild Hunt
Zeus: Master of Olympus
The Elder Scrolls V: Skyrim
The Elder Scrolls III: Morrowind
Red Dead Redemption
Batman: Arkham Knight
Titanfall 2
Assassin's Creed II
Defender's Quest: Valley of the Forgotten
Dust: An Elysian Tail
Grand Theft Auto IV
Fallout 2
Shovel Knight
Fallout 3
Fallout New Vegas
Spells of Gold

Not in any particular order.

No Order:

Gothic 1&2
Elder Scrolls Daggerfall and Morrowind
Planescape Torment
Baldur's Gate 2: Shadows of Amn- Issue with 1 is that low level D&D combat, leveling and skills aren't fun.
Witcher Series
Mount and Blade Warband
Fallout 1,2 and New Vegas
Arcanum of Steamworks and Magick Obscura
The Bard's Tale 1-3 which are available nowadays as Remastered.
Titan Quest
Grim Dawn
Diablo 2: LoD
Might and Magic 6-8
Wizardry Series
Classic Mechwarrior games
Stalker: Shadow of Chernobyl and Call of Pripyat
Blood: One Uniy Whole Blood
Ultimate Doom
NOLF 1&2
Return to Castle Wolfenstein

StarCraft (PC)
Super Metroid (SNES)
The Legend of Zelda: Link's Awakening (GB)
Mother 3 (GBA)
Langrisser II (MD)
Super Mario All-Stars w/ Super Mario World (SNES) or Super Mario Bros. 3 (SNES/NES)
Saturn Bomberman (SAT)
Fallout 2 (PC)
Rocket Knight Adventures (MD)
Baldur's Gate w/ Expansion (PC)

Sonic Classic Heroes (Hack)(MD) or Sonic 2 (MD)
Heroes of Might and Magic III (PC)
Super Mario World 2: Yoshi's Island (SNES)
Power Strike II (SMS)
The Typing of the Dead (PC/DC)
Panorama Cotton (MD)
Final Fantasy VII (PS1/PC)
Contra: Hard Corps (MD)
Seirei Senshi Spriggan (PCE CD)
Mole Mania (GB)

Wasn't even aware there was one, i just keep popping in the PS1 port lol

Couldn't agree more. I scewed up a few of my O levels due to staying up all night with DM. What a terrific game. A damn fine list. I think lots of those would be on my 20-30 :)
Sorry. I wanted to get some ideas of things to play that I have missed, from like-minded gamers :)
Great list BTW

I'm not giving them any particular order. These games each have their strengths and I have more favourites, but these were what came to mind.

Borderlands 2 (PC)
Dark Souls (PC), the other two are awesome as well.
Detroit: Become Human (PS4)
Dragon Age: Origins & Awakening (PC)
Mass Effect 2 & 3 (PC)
Minecraft (PC)
NieR Automata (PS4)
Saints Row: The Third (PC)
Starcraft II (PC) and its expansions.
Spyro series (PS1 & GameCube, the original three and A Hero's Tail)
Super Mario Odyssey (Switch)
Super Smash Brothers Melee (GameCube)
Team Fortress 2 (PC)
Terraria (PC)
The Elder Scrolls IV & V (PC)
The Legend of Zelda: Breath of the Wild (Switch) along with a bunch of old ones like Wind Waker, Twilight Princess
The Talos Principle (PC)
The Witcher 2 & 3 (PC) one was alright but its simply dated.
Warcraft II & III (PC)
World of Warcraft (PC) up to and including the Wrath of the Lich King expansion.

I know I sort of cheated by including series or parts of series.. but oh well. There are more such as the older Pokémon games, Bioshock series, Batman Arkham Asylum/City, GTA 5, Payday 2.. but at some point I had to wrap up the list.

OOTP Baseball-PC (listed first despite not necessarily being my all time favorite of any genre but it's the one I have played the most hours on by far as I've been playing it continuously for about 12 years now). Below this I'm trying to list in order of favorite.

Fallout 4-PC
Fallout NV-PC
Fallout 3-PC
Fallout 1-PC
Gothic 1-PC
Gothic 2-PC
Fallout 2-PC
Betrayal at Krondor-PC
Legend of Zelda III - SNES
Legend of Zelda I - NES
Sid Meier's Civilization IV-PC
Sierra Front Page Football 1998-PC
Motorsport Manager-PC
Divine Divinity-PC
Sid Meier's Civ IV Colonization-PC
Sid Meier's Alpha Centauri-PC
Age of Empires I
Skyrim-PC
Morrowind-PC

Just in alphabetical order, out of what I played. Some may well be seen through nostalgia-tinted lenses.

First pass:

Betrayal at Krondor
Deus Ex
Heroes of Might and Magic IV
Homeworld 2
King's Bounty: The Legend
Might and Magic VI: The Mandate of Heaven
Planescape: Torment
Quest for Glory II: Trial by Fire
Star Wars: Knights of the Old Republic
Star Wars: Knights of the Old Republic II - The Sith Lords
StarCraft: Brood War
The Settlers II: Veni, Vidi, Vici
The Witcher: Enhanced Edition
Transport Tycoon Deluxe
Vampire: The Masquerade - Bloodlines

Hmm, need 5 more, so second pass:

Neverwinter Nights: Hordes of the Underdark
Stunts
Supaplex

Two more? Hm...

Gothic
Gothic II

Also in that third pass, but just missing out since I can't pick a single Gothic:

Sid Meier's Pirates! (2004)

No order and i really don't remember now so i will try to make a list for the first time.

Stalker call of pripyat
Stronghold crusader
Stracraft broodwar
Gothic 2 night of the raven
Prey
Vampire the masquerade bloodlines
Rollercoaster tycoon 1 deluxe
Commandos 2
Earth 2140 trilogy
Oblivion
Mount and blade warband
Recettear an item shop's tale
Cultures
Flatout 2
Prince of persia warrior within
Mafia
Higurashi when they cry hou or maybe spellforce 2 instead but still need to play spellforce 1
Star wars battlefront
Grand theft auto San Andreas
Sonic 3 and knuckles

Strictly a PC player so yeah they are all pc games.