I'll be listing these in order of ascending price, since you may be able to get several good games for less than the price of some entries on this list. ALL PRICES IN CAD$
Literally negative in price - 5m/session - Any number of players - Co-operative - STRONGLY RECOMMENDED - many hours played - Not available on steam
This is a price comparison and history tool that will tell you before you buy a game whether it regularly goes on sale for three dollars despite theoretically being priced at thirty. You should always check ITAD before buying a game; you might end up getting it for a quarter the price by buying on a different store. Cheapshark is similar but gives you less historical data, which I find useful in deciding whether to wait for a game or buy now.
FREE as in beer - 10m/session - 2-4 players - Competitive - STRONGLY RECOMMENDED - 5 hours played - Overwhelmingly Positive on Steam
It's a silly shooter with movement tech intended for fun more than to be seriously competitive. Different levels have different gimmicks - sniper rifles at a thousand paces, slashing each other with katanas, freezing each other in place with tasers so that your opponent gets crushed by a giant trash compactor, or whacking each other with thrown oil barrels. There are hundreds of levels and most of them take less than 15 seconds to kill your opponent on. Every gun is high lethality and you get one clip per weapon. If you miss your shots, better get a new gun pickup. Or die. You could also die.
This has been my #1 game lately simply because it's so damn fast and easy to hop in and out of. A full first-to-4-victories match takes about ten minutes, which means you can do a best-of-three of those in half an hour - or stop after the first match if you're just not feeling it right now. Lots of silly moments, lots of fun winning or getting crushed by your enemies. Feels energetic and is a great appetizer for other forms of gaming.
Has paid DLC cosmetics to support the developers, but the whole game is mechanically available from the moment you download it. If you have ever enjoyed a shooter, you should be playing Straftat.
FREE as in beer - 1h/session - 2-8 players - Competitive - lightly Recommended - 1 hour played - Overwhelmingly Positive on Steam
This is competitive multiplayer solitaire. It's all about being able to clear your deck faster than your opponent consistently. First to call NERTS by getting rid of their pool of cards to clear wins the round. Each round scores points: first to 100 points wins. Between each round a little theme song plays and gives you a break; I found it kind of a silly touch at first but after a few rounds of fast-paced scrambling for points you start to appreciate the breaks. Takes a little picking up but at the end of my first session I was managing alright against another newbie.
The longer session length and brain-demanding gameplay have made this one less of a go-to for me, but it's still worth some time out of your day.
FREE as in beer - several hours a session - 2 players - Technically competitive, but really it's an art program - lightly recommended - 6 hours played - Overwhelmingly Positive on Steam
Build your own monsters as if you were playing a card game like Magic the Gathering. Draw the art for the card yourself with a doodle and fight against your opponent's creations. Takes a while to draw the art for all the cards in your deck, but you get to see what your opponent's sense of style is like. And some of the cards are inevitably really silly. A fun game to spend a few hours on a weekend on. The card mechanics are not robust, but at least you get to play that card of seaweed you drew.
FREE as in beer - several hours a session - 1-4 players, but a little glitchy with larger games - competitive or co-op - lightly recommended - unknown playtime, but many hours - Mixed reviews on steam due to shitty port of browser code
It's Tabletop Simulator but free and with a worse selection of games. I recommend Cult as a good game to play with this. Some games won't load due to having too many pieces; why this happens I have no idea. If you own Tabletop Simulator, use that.
Multiple hours to a session - 2 players - Co-op - Sales for $2.50 CAD - Recommended with partial info - 83 minutes played - Overwhelmingly Positive on Steam
I know you have Portal 2 sitting on your computer from when you played through the singleplayer campaign years ago and I know you have not touched the co-op mode. You should play the co-op mode. It's genuinely fun, has some interesting puzzles, and requires actual teamwork to get through. You also have plenty of time to figure out each puzzle at your own pace, unlike some games I don't recommend (cough cough we were here cough cough).
Playing through the first two test tracks was really fun for me, and I expect the quality to continue.
1 hour a session - 1-4 players (with limits) - Co-Op - Sales for $4 - Strongly Recommended - 7.5 Hours Played - Very Positive on Steam
A one to four player beat-em-up in the style of Left 4 Dead but with swords instead of guns. Play as a bitchy elf woman, equally bitchy fire sorceress, dwarf with a big hammer, or bearded fighter with a magnificent hat. Or that other guy, the witch hunter. Nobody likes him.
Chaotic combat of mostly mooks with some elites sprinkled in to keep things spicy. Best played with three or four but works fine with pairs. Great for when you're in the mood to kill a boatload of mooks.
Unfortunately, this game only lets one player on a team be a given hero(ine), so if you have multiple people who strongly prefer to play female characters (as I do as a trans woman) this game only supports 2 female characters being played simultaneously. This may not be a deal breaker for some players, but I mention it so you won't be surprised.
1 Hour a session - 2 players - Competitive - Sales for $4.50 - Strongly Recommended - 10 hours played (so far) - Overwhelmingly Positive on Steam
This is a fighting game turned into a tactical, turn-based chess match. If you've ever played Soul Calibur, BlazBlue, Tekken, or another fighting game, this is like that, but whenever a player has the ability to act (is not in endlag or startup frames) the game pauses to give you time to think about your turn (anywhere from 15 seconds to 15 minutes.)
Plays like you're simulating a spacecraft cockpit - lots of dials, buttons, and switches to flip - but once you understand how the controls work it's a cerebral, intense game of boxing your opponent into a corner where they have no choice but to get comboed - or else reading their moves and doing exactly what they don't expect you to do.
The learning curve feels like a cliff but you don't need to be good at it to have a lot of fun. And at the end of the game when someone has won, the entire game gets played back frame by frame as if it had been played in real time, which produces incredibly fun fights to watch and rewatch.
About 3 minutes of incredibly intense gameplay a session - 2 players - Co-Op - Sales for $6 - Limitedly Recommended - 1 hour played - Overwhelmingly Positive on Steam
This is a game of grace under fire. You have to complete truly ridiculous steps under a very tight time limit, or kaboom. One player manipulates the bomb, the other reads the instructions on how to defuse it and tells the solver how to not blow themselves up. Great for training communication skills with your domme, not so great for casual gaming when you're trying to relax. The gameplay is a well-oiled machine, though, so if you have the courage, this is worth picking up as a novelty. And when you successfully defuse a bomb, the surge of elation is huge and makes you feel very in sync with your partner.
1 Hour a session, or "play by post" - 1-4 players - Competitive - Sales for $6.50, but you'll pay for a bunch of DLC if you want to play from your phone - Recommended - 138 hours played - Very Positive on Steam
This is a card-drafting game where you build your deck over the course of the game, similar to Dominion. Most of the game (seven or eight expansions) is included in the base purchase price... On PC. If you want to cross-play from your phone or tablet you'll have to cough up money for each expansion you want. I recommend Dreamscape as your first purchase.
Great for when you're in the mood for something slower; turn timer of up to 24 hours means that you can also play games essentially by mail in snatched moments. Best when playing with friends you know so they actually get around to their turns, though.
Several Hours a session - 1-3 players serverless, up to 100 players with a server - Co-op or competitive - Sales for $11.50 - Lightly Recommended - 22 hours played - Very Positive on Steam
You versus the cold void of space. Has a great setup period where you're trying to become sustainable in the void, but once you're stable you're going to need to turn to combat to find more fun. An excellent game if you're an engineering or automation type; a little less fun for less gearheaded players. Remember to put yourself in the stasis pod when you log out.
Several hours a session - 1-12 players - Co-op - Sales for $13.50, but it has VIKINGS - Strongly Recommended - 128 hours played - Very Positive on Steam
This is a parry-based combat game with a stellar house-building system that encourages you to make places that feel lived in and real. Bosses, base-building, and bashing zombies in the face. Minecraft but more fighty. Just overall a great time. This game is home to me in many, many ways. Mods add some additional build pieces that feel missing from the base game, but the base game is not shabby by itself. Not good for players who have trouble with food, because the food buffs in this game are completely essential.
This is the best card-drafting game I have played yet, and it's not close. I may be blinded by the cute girls. You choose one of eight princesses to back in a battle to be crowned queen during the game; if your opponent sponsors a princess before you then you can't pick that princess yourself. The backing mechanic makes it deeper than many other games in its class, since there's a midgame turning point to build around and plan for.
Its networking is a chore to set up, involving manually opening a port on your firewall (!), but it's best-in-class for gameplay. I have played this game to death (82 hours!) and bought the $40 sequel because I love its gameplay so much and don't want to deal with the networking issues of the older version. If you, too, have a princess addiction, this is the game for you.