Torchlight 2 is a really fun Diablo-esque RPG that you can play co-op. Several different classes, doesn't require super powerful PCs and SO MUCH LOOT. And if that sounds like a game you'd both enjoy (and if your computers can run it), Borderlands 2 can be wicked fun in co-op!

Other fun co-op games I'd recommend are Don't Starve Together, Terraria, the Trine series, Octodad: Dadliest Catch, Rayman: Origins and pretty much any of the Lego games.

Hope this helps!

If you've got two computers.
Dying Light
Me and the wife have over 100 hours playing it. VEry good co-op game

It should be noted that while you can try to make it work as a co-op game by sharing controls (and I believe it might also be interesting enough for someone just to watch while the other one is playing), it is officially a single player game and not meant to be played with two players. Just to avoid confusion or disappointment!

Quick and dirty list of some of my favorites:

Torchlight 2
Trine 1-3
Starbound
Terraria
Towerfall Ascension (local coop only)
Divinity - Original Sin (Playable on i3-4005U or better laptop with Intel HD)

Lovers in a dangerous Spacetime
PixelJunk Shooters
RingRunner (there's some dual ships for coop)
Guacamelee
Hammerwatch
Sacred 2
Risk of Rain
Torchlight 2

I've heard that Divinity Original Sin is great for co-op. Haven't played it though.

Thank you so much to all of you!

With this list we can go on for a while.

Thanks.