Which Game Under 5$ Would You Buy This Winter Sale?

Well I think Portal 2 is amazing, so you should get that.
Excellent campaign and co-op campaign, plus endless amount of user-created maps, plus free mods like Portal Stories: Mel which is basically a whole new campaign.

Wyv and Keep is on a super sale too... if you like co-op puzzle games. $1.49.. man I wish that game sold better.

Don't Starve, it's an amazing game with a lot of depth and you are getting endless hours of gameplay, as the game is never "ending" and you are going to have a different experience each time you play.
Some fellow users mentioned also Portal 2 and Spelunky, which are really great choices, also in terms of replay value .

Here are 20 games under 5$ that I've played. and I think they're good

Outland $0.99 TC
POSTAL 2 $0.99 TC
Serious Sam Classics: Revolution $0.99
Ubermosh $0.99 TC
Critter Crunch $1.04
Super House of Dead Ninjas $1.74 TC
LUFTRAUSERS $1.99 TC
Shatter $1.99
Downwell $2.00
Aerannis $2.49
Angry Arrows $2.49
Hotline Miami $2.49 TC
Pushcat $2.49 TC
Symphony $3.05
Snakebird $3.49 TC
PAC-MAN Championship Edition DX+ All You Can Eat Edition Bundle $3.74
Spelunky $3.74 TC
Strata $3.99
Cave Story+ $4.94
Shantae: Risky's Revenge - Director's Cut $4.99 TC

I bought Transistor and Grim Fandango, and I will buy (before the end of the holiday sales) also The Talos Principle. Their cost is under 5€.

Of course, if you don't have Portal 2... BUY IT!

Gabriel knight 20th
The bridge
Apotheon
Enslaved
Badland

tomb raider

Grim Fandango HD Remaster!

Not sure about this sale, but usually there are a couple of Assassin's Creed games on sale around the 5 dollar. Medieval 2 Total War and Rome Total War are also worth your time if you like strategy games (not sure about the prices though).

Portal 2 :D

Battleblock or Saints Row 3!

Shower With Your Dad Simulator 2015: Do You Still Shower With Your Dad

Papers Please :)

If you like multiplayer / co-op Castle Crashers is pretty nice (Battleblock Theater developer). It has single player too of course.

Get serious sam 3 full pack. Apparently it still has some multiplayer players too, not sure tho, do a little bit of research yourself if u wanted to buy it for multiplayer.
There's also witcher 2 and skyrim. And if u want to choose from the ones you mentioned, BBT is nice specially if you have someone to play co-op with, other than that saints row is awesome too but I say go for fourth one.

A few people have said "maybe Transistor".

There is no "maybe" about it. BUY TRANSISTOR.
Also Crypt of the Necrodancer.

Faster than Light

1. Tembo the Badass Elephant -- i purchased it the other day and already love it!
2. Crypt of the Necrodancer
3. Monaco -- it's fun for local co-op also
4. BattleBlock Theater
5. Tomb Raider -- i've played it from my bf's library ,great game.You should buy it imo ^^

System Shock 2

Out there Somewhere - short platformer, but really good and worth it even at the full price of $1 / 1 euro.
Tower of Guns - randomized FPS. Also includes randomly picked and insane storylines. Probably one of my favorite games from last year, still firing it up on a semi-regular basis.
Ikaruga - has it's flaws, but is a classic among shmups for a reason
Resonance - one of the better point & click adventures I've played, ever. Also, Logan Cunningham of Bastion & Transistor fame voices one of the characters here, to great effect.
Rogue Legacy - if you like rogue-likes or metroidvanias, consider this one. If you like rogue-likes and metroidvanias, just get this now. It's really a happy marriage between the two genres. Tongue-in-cheek presentation makes it all the more amusing too.
XCOM Enemy Unknown - fits the bill if you like turn-based strategy. Although you'd really want to stretch the budget a bit and get the complete pack instead in my opinion. Enemy Within expansion included in that adds so much gameplay-wise that it's a shame to miss it.
Shadowrun: Dragonflall - if you like turn-based strategy mixed with RPG instead. I can't make up my mind if this or Shadowrun: Hong Kong is the better game, but Hong Kong isn't below $5 so it's disqualified for this thread anyway.
Mortal Kombat Komplete edition - MK has always been a bit of an oddball among fighting games, with all characters having the same basic moves and all. Yet this reboot (in-universe too) manages to take the series back to it's 2D roots and make each character more unique at the same time, making it one of the highlights of the franchise.

edit:

YS - Oath in Felghana - the excellent remake of the somewhat crappy Ys III: Wanderers from Ys. Or Ys Origin. Japanese action-RPGs at their best. Ys: The Ark of Napishtim.is based off the same engine and has similar gameplay, bit it's still a bit over the $5 mark right now.

Darksiders

Rising Storm

Garry's mod

-Dark Souls: Prepare to die edition
(patched with dsfix and dsmfix - so you can play it with mouse and keyboard like skyrim)

-Dungeons of the endless

-Grim Fandango Remastered

Papers, Please.