Hard to put a particular order, so as an unordered list! Excluding multiplayer only games.
Also, no way I could narrow it to 10 :/
There is one exception though, definitely my favorite game is
Ultima Underworld
The rest of these are fairly tied

Zelda: Links Awakening
Silent Hill 2
Super Mario Bros 3
Ultima 7
Nethack
Disgaea
Soul Cradle
Mana Khemia
Phoenix Wright Ace Attorney
Metal Slug 2
Harvest Moon
Seiken Densetsu 3
Secret of Mana
Crono Trigger
space quest 2
Half Life
Super Robot Wars Alpha Gaiden
Demon's Souls (RIP online play, gone is the age of "sticky white stuff"...at least with dark souls 3 now we have "ahead finger but" :/)
Bloodbourne
Drakengard
Drakengard 2
Drakengard 3
Nier
Nier: Automata (what can I say, Yoko Taro is a freaking god)
Elite: Dangerous
Eternal Darkness
If i were to include online games on here
Unreal Tournament 2004 w/ECE
Team Fortress Classic 1.0
Ultima Online 1997 release to "The Second Age" expansion, before they completely re-wrote the game in 2000 for the "Renaissance" aka gutting the fantastic game to be a shallow everquest clone expansion.
Neverwinter Nights Diamond (I know it has single player, but the single player was overwhelmingly mediocre, only it's online was good, but it was REALLY good)
Ark: Survival Evolved before the patch that allowed dino and item cross ark transfer
"The Culling" before the developers decided to gut the core melee combat in favor of adding in tons more flashy guns and ranged weapons and making them super easy to get.