these are the games i've 100%ed in (mostly) alphabetical order, and i highly recommend each of them:

The Awesome Adventures of Captain Spirit †
Call of Duty: Black Ops 2
Cats Hidden in Around the World, Bali, China, Georgia, Italy, Maple Hollow, Paris
Danganronpa: Trigger Happy Havoc
Danganronpa 2: Goodbye Despair
Danganronpa Another Episode: Ultra Despair Girls
Danganronpa V3: Killing Harmony
Emily is Away
Firewatch
GRIS
The Henry Stickmin Collection
Hotline Miami
Lego Indiana Jones †
Lego The Lord of the Rings
Lego Marvel Superheros
Lego Pirates of the Caribbean †
Milk inside a bag of milk inside a bag of milk
Milk outside a bag of milk outside a bag of milk
missed messages
Montaro
OneShot
Papers, Please
Return of the Obra Dinn
Steins;Gate
Spyro: The Reignited Trilogy *
The Stanley Parable
Undertale †
Who Pressed Mute on Uncle Marcus?

games marked with a dagger (†) are ones that do not have achievements on steam, but ones that i still earned 100% completion on.
games marked with an asterisk (*) are ones where i got every achievement, but didn't get 100% completion as defined by the game.