Assuming that "masterpiece" refers to the quality and impact the games had in their time (not how well they aged) some of my picks would be:

• Baldur's Gate 2 + ToB
• Star Wars: KotoR
• Morrowind
• Read Dead Redemption 2
• The Witcher 3
• The Last of Us 1+2
• God of War
• Shadow of the Colossus
• The Legend of Zelda: BOTW
• Mass Effect 1+2
• Disco Elysium
• Half Life 2
• BioShock 1
• Diablo 2
• Fallout 2

I don't know how objective this list is. Some picks are definitely subjective and fit more in a "flawed masterpiece" category of games that had a large impact on how I perceived games but that may not be so widely acclaimed as some others on this list.

How come no one has mentioned “Life is strange” yet? Also, “A plague tale”.

My Picks...

Deus Ex (So many games try to be this and fail)

Cyberpunk (This one eventually measured up)

Alpha Centauri (Innovation mixed with familiarity and setting)

Fallout 2 (they're all good. Fallout 2 is special)

Kotor (Star Wars story telling in a beautiful way)

Baldur's Gate 2 and 3 (I'm stunned that 3 was a worthy successor)

Homeworld (One of the World's truly beautiful games)

Team Fortress 2

The best teamshooter game to date, endless copy cats that suck ass.

Supergiant games' holy trinity: Bastion, Transistor and Pyre.

Also, the only Borderland games 1 and 2; don't believe the lies there are no more true Borderlands games and no there most certainly is no movie.

There's also one other, but you'll need a crowbar or a gravity gun in hand for me to tell you about it.

Shadow of the Colossus

Hades

Hollow Knight

Noita

Super Metroid

Prey (2017)

DOOM (2016)

Factorio

Stardew Valley

For me it's Journey. That game gave me an emotional experience I've never had in any other.

Chromehounds was the greatest mech game on shitbox 360 and you can't change my mind.

The sheer variety in player created metas was glorious to behold. Sure, you could play how the game encouraged you to play and hang your weapons in "normal" configurations. But you could also bury whole teams in indirect fire with a triple double from across the map. You could build a little punchy boi buggy with a dick piston, cockpit, wheels, and nothing else. You could even try to sweat the meta in the chicken leg howitzer or the turtle up in the armored crab.

The only limits were creativity and spacer availability lmfaooo

Thomas Was Alone

I've never felt so much for quadrilateral shapes.

I'm going to take this as "games that I never see anyone question their quality." (I don't even like all these games myself)

• Sonic 3 & Knuckles

• Kirby Planet Robobot

• Doom 2016

• Street Fighter III: Third Strike

• Pac-Man

• Balatro

• Steins;Gate

• The House in Fata Morgana

• Castlevania: Symphony of the Night

• Gran Turismo 4

• Mario Kart 8 Deluxe

• Mega Man X

• Mega Man X4

• Super Mario Bros. 3

• Hollow Knight

• Bloodborne

• Elden Ring

• Balder's Gate 3

Bastion, Hades, Disco Elysium, Planescape: Torment, and Tyranny (even if the last act is rushed in the last two) come to mind for me

There is no "objective" when talking about subjective terms.

My personal, SUBJECTIVE favorites are Mass Effect, Titanfall 2, Subnautica, Stardew Valley, Ori and the Blind Forest, Dave the Diver, Balatro, and Portal 1 and 2

Hotline: Miami

Beyond Good & Evil

Final Fantasy X

Celeste

Hades

Ace Combat Zero/5

Way more to choose but top of my head

Edit:

Halo

Titanfall 2

M&B: Warband

Evolve (yes I said it I’ll go to the mat over it)

Immortality

Factorio, Terraria, Half-Life 2, Portal 1/2, Limbo, Night in the Woods, Lil Gator Game

Clair Obscur has been the best game I've played in a long while, absolute masterpiece

Hollow Knight is peak

Nethack

Super Metroid

Well, none because favorites are super subjective, but I'll shout out my favorites because no one else did:

1. The Wonderful 101
2. Bayonetta
3. Ninja Gaiden II
4. God Hand
5. Viewtiful Joe
6. Catherine
7. Gravity Rush
8. Guilty Gear XX Accent Core Plus R
9. Under Night In-Birth II Sys:Celes
10. Persona 4 Arena Ultimax
11. Crimzon Clover: World EXplosion
12. Ketsui: Kizuna Jigoku Tachi

Curious to hear what the criteria for "masterpiece" is, otherwise I think it is just peoples' subjective opinion of what makes a great game that they also think others might agree about being a great game. Genuinely curious, interested in discussion, not saying this to shut down any of the answers here.