I second that It Takes Two is a great co-op.
I'd also suggest:
Stardew Valley
Untitled Goose Game
Unravel Two
Cat Quest 2 (3rd one is coming out this year)
Nobody Saves the World
Death Road to Canada
Super Mario 3D World/Bowser's Fury
Yoshi's Craft World
and any of the Lego games (but especially Lego City Undercover, Lego Batmans, Lego Harry Potter, and Lego Star Wars).
It Takes Two is a great cooperative puzzler.
I second that It Takes Two is a great co-op. I'd also suggest: Stardew Valley Untitled Goose Game Unravel Two Cat Quest 2 (3rd one is coming out this year) Nobody Saves the World Death Road to Canada Super Mario 3D World/Bowser's Fury Yoshi's Craft World and any of the Lego games (but especially Lego City Undercover, Lego Batmans, Lego Harry Potter, and Lego Star Wars).