Good thread! I have a Steam account for several years and my most favorite games on Steam are:
1. Cogmind - the roguelike where you are playing as a robot, who has found itself in the unfamiliar facility and then try to escape. You can learn about story of this place and its inhabitans and gather another kind of information at the terminals (there are a lot of lore in this game!). You can meet some funny robot buddies and have fun quests and conversations with them. You can hack another robots in the couple of ways. You can use a TON of weapons of different kinds. You can attach parts of another robots to yourself and re-build yourself in a different ways. You can try several gaming styles and achieve several endings. Also tiles in this game are very nice and - surprisingly for roguelikes - there are cool visual and sound effects, especially for battles!
2. Dark Souls 2 & 3 - I think that most of people heard something about them, but if you don't, I highly reccomend to take a look! Very briefly: It's hard slasher game series with interesting and tough battles and very cool (for my taste) visual style.
3. Invisible, Inc. - pretty hard tactical turn-based strategy, where you manage a team of special agents, who sneak into facilities of different cyberpunk-style corporations and steal money, information, items, robots etc. . The main difficulty is that enemies kill your agents from the first shot every time when they see them. And you mostly have non-lethal weapons, which just knock out enemies for a couple of turns. So you should be very sneaky, mostly avoid battles, distract the enemies in the proper time and hide your agents well. Also alert level is constantly increasing, and more tough enemies appears. And levels are generated randomly so you can't just memorise them and you should plan your operations in some robust way as well as be prepare for improvisation. It is permadeath-style game and in highest level of difficulty you have no opportunities to revert any of your turns, so you can have a lot of adrenaline when situation becomes hot. I like as well cyberpunk visual style of this game.
Ooops... seems like I've already been too much verbose while recalling my favorite games, so I'll try to be more laconic now and just briefly mention my favorite visual novels, in which I liked to play at Steam when I was too tired by suffering in the hardcore kind of games:
VA-11 Hall-A: Cyberpunk Bartender Action, Life is Strange, first two games from Walking Dead series, The Wolf Among Us, Night in the Woods, Angels of Death, The Cat Lady, Downfall, Space Pilgrim series, Everlasting Summer.
And... I just can't not to mention yet two more very fun and cool games:
- Terraria (sandbox-like game) and
- Crypt of the NecroDancer (rhythm game)
Well, well... I should stop myself now finally