Getting really tired of online games. Can't stand it anymore.

I haven't played any of the ones you mentioned, but FTL is an amazing offline 2D game and conveniently available in the current Humble Bundle.

2D??? Try some Shank 1 and 2, Trine 1 and 2 ... there are lots of 'em Braid, Super Meat Boy, Mark of the Ninja, VVVVVV btw those were all in bundles so you can get your hands on any with no trouble.

Castle Crashers,Terraria,hotline miami,Binding of isaac,Thomas was alone,Little Inferno,Rogue Legacy,Faster than light,Fortix,Fortix 2,Awesomenauts,Cave story+,Super Meat Boy

Rogue Legacy

Rogue Legacy, Terraria, Mark of the ninja, and Trine 2 what I got, all awesome!!
Faster than light, Fortix, aaaaand maybe Symphony are good ones too.

If you like DF, definitely Terraria?

Avadon: The Black Fortress is made by the same company who made Geneforge and is very much like Geneforge.

A Velley Without Wind 1 and 2 (will give you hundreds of hours each if you enjoy them type of games.)

Cave Story+

Binding of Isaac

Basement Collection

Limbo

Shank Series

Trine 1 and 2

Terraria

Intrusion 2 (Has great boss battles)

McPixel?

Snapshot

Toki Tori (Never tried 2)

Awesomenauts (Although this is online)

Capsized

Hotline Miami

Mark of the Ninja

Offspring Fling

The Showdown Effect (Online again)

Thomas Was Alone

Cargo Commander (Under rated game)

Gun Monkeys

Not 2D but could interest you : Bastion , Edge , Rush , Magicka , Super Hexagon , Don't Starve , Fortix 1&2 , Beat Hazard , Hotline Miami

Battletoads

FTL is really awesome, I'm getting sucked into it!

Try any shmup on Steam that isn't called Sine Mora or Gun Bullet Children.

For shmups I particularly recommend Exceed 2nd, Satazius, and GundeadliGne.

Other than that
Rogue Legacy is amazing.

Bleed is a great run and gun shooter (though I recommend playing on arcade difficulty)

They Bleed Pixels is probably one of the best action platformers I've ever played.

Some 2D games that I would recommend:

• Awesomenauts

• Bad Rats

• Bit Trip Runner/Runner 2

• Braid

• Castle Crashers

• Cave Story

• The Binding of Isaac + DLC

• Don't Starve

• Dust: An Elysium Tail

• FEZ

• Trine/Trine 2

• Fortix

• Secret of the Magic Crystals

• Plants Vs. Zombies

• Klei's games

• Rayman games

• Hell Yeah!

Deadly 30

Dota 2D

Touhou
eXceed
Ys (all of them, both good story and really good gameplay with good visuals and running so smoothly that you won't believe it)
Cthulhu Saves the World (funny with lot of jokes but it can get annoying after some hours)
Mark of the Ninja (surprisingly the controls are kinda neat and sweet, easy to handle, at least with a controller)
Offspring Fling!
Plants vs. Zombies (if I don't dislike a zombie game then you can buy it)
Snapshot
Sugar Cube (really depend of the person)
Toki Tori (same as Sugar Cube)

Here it's a fast check. I didn't listed just good games because they might be not focused on the "fun" part, like Cave Story or Fortune Summoners which are more about their good stories even if their gameplays are not bad either.

Gnomoria, Don't starve, Shank, Shank 2, Mark of the ninja, Deadlight, and MOOOOOORRREEE

TERRAAARIAAAA