The best game they've never played...

I even bought Blood Dragon and Juares as a pack, they're high on my to-play-soon list =)
Thanks for your suggestions ;)

As for your games - New Vegas definitely deserves a closer look =)
Binary Domain is a cool take on cover shooters, this game has a great relationship system, which alters the gameplay =)
Hydrophobia is an interesting game, if you actually have a hydrophobia (like I do :D)
Metro Last Light is an awesome post-apocalyptic game, it has a great atmoshpere.
Portal - this is an all-time classic. Really solid puzzle game, with great story and tons of sarcastic humor =)
Vampire: The Masquerade - Bloodlines. Hands down the best vampire RPG out there. Prohint - play as Malkavian for bonus laughs :D

War of the Roses

I can't believe you've still not played Portal 2 D:

L4D2 man! Play it! With friends! (better teamplay and more fun) :D

Bastion, Amnesia The Dark Descent, Left 4 Dead, Super Meat Boy.

Have fun!

Everything in your library, you just don't play enough.

Braid is unbelievably good, and easy to get into. Check it out.

Half Life 2 is my favorite game ever. Still lots of fun after all these years.
Play sword and sworcery on your phone, in the dark, with headphones in

VVVVVV, Sleeping Dogs (ASAP, one of my favorite games), Shank (TONS of fun), Red Faction Armageddon, Metro 2033, Mark of the Ninja, Max Payne 3, LA Noire, Deathspank, Darksiders 1, Cave Story+, Burnout Paradise, Bioshock, Both Batmans you got, Bastion.

Half-Life 2: Lost Coast? It's pretty much a short demo, but it's the only thing I've played much of.
Other than that, Nihilumbra looks interesting, and the tiny bit of Dino D-Day I've played was fun.

VVVVVV, Star Wars The Force Unleashed 1+2, Singularity, Red Faction Armageddon and Guerrilla, Prototype, All of those Prince Of Persia games, Oddworld: Abe's Odyssey, Mirror's Edge, Max Payne 1+2, Mark of the Ninja, Lost Planet 2, LA Noire, Just Cause 2, I Am Alive (Pretty interesting game mechanics on here), Half Minute Hero, GUN, Fez, Farcry 3, Fable, Evoland, Drakensang, Dead Rising 2, Darksiders 1+2, Castlevania, Castle of Illusion, Bully, Assassin's Creed 2.

Gosh man, so many games, such not enough playtime!

I would say Don't Starve. Amazing game! Give it a try ;)

VVVVVVV, Trine 2, The Adventures of Van Helsing, Sleeping Dogs (ASAP, great game), Septerra Core (If you're into old school games), Red Faction Armageddon, Mirror's Edge, Mark of the Ninja, Left 4 Dead, Just Cause 2, GTA4, Final Fantasy 7+8, Don't Starve, Dead Space, Deadlight, Darksiders, Burnout Paradise, Batman Arkham Asylum, Batman Arkham City, Bastion, Assassin's Creed 2 (I assume you have it on PS3/Xbox, but for the graphics get it on pc).

Epic collection by the way!

The Darkness 2, Sniper Elite V2, Shank (ASAP! Tons of fun!), Need For Speed Undercover, Metro 2033, Max Payne 2, Half Life 1+2, Fez, Bioshock (obviously), Amnesia The Dark Descent, L.A. Noire, and Trine.

Nice looking collection by the way!

Universe sandbox is actually pretty fun to play around with. Plants Vs Zombies is very satisfying to beat. Psychonauts is fun but a little slow paced IMO. You gotta play Oblivion!

Sniper Elite V2, Saints Row The Third (ASAP!), Darksiders, Batman Arkham Origins.

I'm tempted to say "Borderlands 2", but I didn't like it as much as the first. Give it a try!

The Darkness 2 (ASAP), Red Faction Armageddon, Hard Reset, Far Cry 3 (ASAP!!), Batman Arkham City. Give them a try! The Darkness has one of the most interesting storylines I've played in a long time.

Play more Terraria and Bastion, they're both really good.

The Adventures of Van Helsing, Deadlight, and try out Need For Speed Undercover. It's the only other NFS game worth playing since the original Most Wanted.

Trine, Red Faction Armageddon, Just Cause 2, Darksiders... But they're all better with a controller.

The Witcher 2, Mirror's Edge, and add some time to Red Faction Armageddon. Have fun mate!

Mafia II, Outlast, Spec Ops: The Line, To the Moon.

FTL, maybe FEZ and Worms: Armageddon with some friends/relatives.

Hm...gotta say either Super Hexagon or The Void.
Super Hexagon is very fast-paced, The Void is bleakly pretty but is very, very bizarre (as in, the devs must have been on drugs bizarre...something in common with all of their games, actually) but they're both very hard and unforgiving.

Sid Meier's Pirates

Most people will say Bioshock.

The Darkness II, Deadlight, Bioshock, Arma 2: DayZ Mod

Bioshock Infinite DLC, Arma 2 (Only if you love super hardcore military similator/shooters.), and The Ship (yes, it was free for a while, but it is still a pretty good game)

The Swapper

Fantastic puzzle platformer. Doesn't take that long. I finished it in an evening. Also drops cards.

Anomaly: Warzone Earth is alright.

The Darkness 2 duuuude, play it!!

Uplink, old school, but fun stuff.

You should play Borderlands