Short Steam games (6-7 hrs max to finish) that you can recommend?

You don't really finish a game until you have all achievements. Just sayin'...
Btw, "The Shopkeeper" is very short and getting all achievements is easy.

The Vanishing of Ethan Carter

The Dream Machine

Papo & Yo

I Have No Mouth, and I Must Scream

The Darkness 2

Brothers: a tale of two sons

Spec Ops: The Line (Short with an awesome story)

Gunpoint (3 hours to finish)

To the moon (like 4 hours to finish and 1 hour for crying)

Check out HowLongToBeat

From your library I would suggest: Amerzone: The Explorer's Legacy

• Mirror's Edge
• Metal Gear Rising: Revengeance
• Spec Ops: The Line
• Far Cry 3: Blood Dragon
• Fez
• Brothers: A Tale of Two Sons
• Valiant Hearts: The Great War
• To The Moon
• Bastion
• Transistor
• The Vanishing of Ethan Carter
• Limbo
• Papers, Please
• Shovel Knight
• Alan Wake' American Nightmare

Source: http://howlongtobeat.com/ Search, Platform: PC, Sort By: Most Popular, first 5 pages.

Kane & Lynch: Dead Men

Kane & Lynch 2: Dog Days

Medal of Honor: Airborn

Condemned: Criminal Origins

Machinarium

Offspring Fling!

Medal of Honor (2010)

Crysis Warhead

Hydrophobia: Prophecy

Trapped Dead

To the Moon
Thomas Was Alone
6180 the moon

All nice simple indie games that are quick to beat.

bit dungeon 2

Adventures of Shuggy
A short, cute (but not childish) platformer featuring a purple vampire.

The Stanley Parable
The Fall
Really enjoyed those two.

Fortix
Afterfall: Insanity (far from perfect, but I found the story interesting enough to complete)
YS: Origin maybe, if finishing with one character is enough. Then it should last you up to 3 months ;)
Astebreed - it's a scoring-based shmup so being short for a single playthough is kinda standard for the genre. And if I can reach the last boss on my first playthough, finishing it in 8 hours should be very much possible. (I still have to get back to this one really, it's pretty good despite being on the easy side)
Jazzpunk was already mentioned. It's really short but the absurdist humor make it very memorable.
Mortal Kombat 2011 - story mode can be completed in about 8-10 hours easily. Of course, being a fighting game you may be spending a lot more time in arcade mode/online mode, but hey...

Deadlight
The Cave

Gone home is awesome

The 3 first Blackwell games are about 3-4h/each
DOOM 1, 2 & Final DOOM are about 4h/each
Freedom Fall is about 1½h
Lume is ½h
MURI is 1h
Pizzle Agent 1 & 2 are about 2h each
Braveland is about 3h
Thomas Was Alone is about 2h
The Typing of the Dead: Overkill is about 3h
Zeno Clash is about 2h

Kane and Lynch 1 and 2. I liked em enough, you could finish those in 6 hours

Shadowgrounds

Crysis 2 Maximum Edition

Red Faction

Half-Life: Opposing Force

Half-Life: Blue Shift

Thomas Was Alone

Brothers - A Tale of Two Sons