Okay, bullet formatting is taking too long. Dead or Alive 5 (mostly here because of so few options, even by fighting game standards scantily clad).Street Fighter x Tekken (tag team, but it has been, hypothetically, temporarily pulled from Steam until the Windows Live issue is fixed).Descent series (bad for anyone prone to motion-sickness).System Shock 2 (horror, might want to wait on the hypothetical remake with fixed multiplayer).Tiny Brains (I only played the first part of it, but I like what I played) FPS-ish: The Secret World Legends (free-to-play, same as previous, low-population MMORPG+puzzles).Uru Live / Myst Online (free on donation-run servers, kind of MMORPG-ish puzzle game.Orcs Must Die! 2 (gives a breather to talk and coordinate between waves of orcs).A Virus Named Tom (made by a couple, but very hard during the last section).Portal 2 (physics puzzles designed around 2 people).

If a touch of horror (more tense, less scary) with a bit of meaning (about passions) I would add The Cave. If it could be kept up with by both people, I would also add Orcs Must Die! 2. My top picks for 2-player co-op for a non-gamer who is still able to coordinate in a video game (can navigate 3D games, use a gamepad, etc.): the Trine series (physics-oriented fantasy platformer, slightly more fun with 3 players), Beyond: Two Souls (hard to describe without spoiling this one, but very story-oriented, with one person playing a girl and the other their “imaginary friend”), Lara Croft and the Guardian of Light (action+puzzles designed around 2 players), Clandestine (1 person 'hacks,' the other does the sneaking), the We Were Here series (the first game is free on Steam, and requires exactly 2 people to solve), Never Alone (2D platformer), and Divinity: Original Sin (top pick for a 2-player co-op RPG). and assuming specifically is good for 2-player co-op. and assuming online-ready co-op only (via any method). I am just not sure how best to narrow it down to exactly what you are looking for. I have a looot of experience with co-op games.

System shock 2 co op campaign