Hell by ahintoflime
Hell was made for the A Game By Its Cover Jam, in which developers made games inspired by a bunch of interesting (fictional) box art. They could choose to add 'diversifiers' to make things a bit more interesting, and that's exactly what ahintoflime did by embracing the 'Fuck this jam' optional theme. That tasked devs with making a game in a genre they hate, and judging by the description, ahintoflime either hates adventure games or walking simulators, not that this is much like the latter at all. Hell much more closely resembles old Mac adventure games like Shadowgate, Uninvited or Manhole, placing the player in a wonderfully authentic 1-bit world full of strange characters, witty descriptions, and an important egg.
Elsewhere by Matt Miller, Ian Swain, Fern Ritter, Chao Fang, Jake Van Heemst
Elsewhere plugs you into an attractive, glitchy noisescape in which you'll lose yourself, chat to odd creatures, and generally try to avoid nightmarish creatures. There's a lot of wandering in the dark involved, but it's worth getting to grips with that as this is a truly unusual fantasy world that looks like nothing else out there.
A Bright Light in the Middle of the Ocean by Fi Silva
This gorgeous walking sim-ish game is a little more involved than many in the genre, thanks to your ability to interact with a handful of things. One of those things is a nifty spyglass, while the other is a big lighthouse that will spin around warning sailors about rocks and that. Really, the spyglass is the thing, as it lets you zoom in on the busy background of A Bright Light's chunky, colourful, serene little world.
Short Trip by Alexander Perrin
Whack this hugely impressive game into a browser tab, and enjoy a few minutes' peaceful journeying, in Alexander Perrin's adeptly hand-drawn side-on adventure set on a tram network. You're the driver, see, and after you hop onto the tram you'll have to remember (or not remember: it's not like you'll be punished) to slow down at stops to let people off, and people on. The countryside between those stops is stunning to observe, but the sound design might be even better, Short Trip's rickety rail noises and background atmosphere doing the heavy lifting in a game that will wholly transport you to another place and time.
Five Secrets by Kitfox Games
You can't teach your grandmother to suck eggs, but you can place five specific items into a ritual circle and summon her ghost, as the old saying goes. The message she imparts after a successful summoning seems to depend on what you chuck into the chalk circle; you have to balance certain energies (light and dark etc), but as each item has its own unique weight in Five Secrets, there are many different ways, many different combinations in which to achieve this.