Vessel

Nice little puzzle-platformer. I enjoyed playing the first few levels. Well thought out, standard learn-as-you-progress in the game.
Unfortunately, after only a few levels, I became increasingly frustrated by not being able to physically do whatever task was needed to pass an area. I'm an old-school gamer, I enjoyed figuring out the first puzzles, but then ultimately the game just became either too obtuse (requiring looking up walkthrough cheats), or too much speed and dexterity to win. Couple that with an occasional "things don't work because you clicked one pixel off" and you have a platformer that is unforgiving and not fun to grind through.
I still give Vessel a thumbs-up since most people will likely enjoy at least some of the first content. Sadly, I feel I was just starting to get into the game before it became too difficult. Luckily I picked this one up on sale cheap.

Puzzles are fun, fluid physics work well, and I really dig the "2D/3DHybrid Art Style", gives it a very cool and unique look.
Good game.

Vessel is a physics puzzle platformer primarily focused on liquid manipulation.

super nostalgic and super fun

straight to the verdict
It's rather well made and enjoyable puzzle game featuring mechanics not oft seen in other games. You should preferably play this with a controller although mouse + keyboard are also possible.
¿What is this game? ¿What do you do in it?
Vessel is a 2-D side scrolling puzzle game featuring fluid physics.
Set in a steampunkish universe you play as a genius inventor who needs to remedy the mischief caused by his own greatest invention: man-sized fluid creatures (called fluros) that have behave intelligently enough to have become integral parts of industrial labor. Recently they have ascended beyond there mere servant status though and started to evolve new forms on their own, even acquiring a rudimentary form of sentience.
The worldbuilding and story are neatly done provide context to your unique abilities and the situations that you'll encounter throughout the world.
The puzzles I would describe as of the experimental lockbox kind meaning you'll need to discover the right kind of interaction between various creatures, switches and your own toolkit to advance. You do this by simply experimenting and taking note of the interactions in the given room. Somehow you need to chain them together and exploit them. There's also some lightweight plattforming here and there. Puzzles can be reset at any time, there's frequent check points and rarely time pressure or super precise input required all of which makes for a relaxed moment to moment gaming experience. Notably Vessel makes ample use of physics, specifically fluid dynamics. To give you an idea what that means: in a particular puzzle you might have to lure a fire creature to a nearby ledge, then spray it with water at the right time to generate steam and finally suck the steam into a nearby turbine to activate a generator. The path that water and steam take is computed dynamically depending on physical parameters like volume, velocity, obstacles, etc. as opposed to being prerendered (how most games would do it out of convenience).
strong points
* puzzles are generally well crafted and encourage you to experiment with the surroundings until you find the proper mechanism. The difficulty curve increases steadily as more and more tools are introduced. While there's generally 1-2 intended ways of solving a particular puzzle you might occasionally stumble into a non-intended, emergent solution.
* the physics engine behaves quite well which enables the exploitation of spraying liquids, filling containers, etc. This was a crucial thing to get right and the devs did it.
* the artistic presentation (art style, sound & music, etc) is pleasant and fits the game's mood and narrative
weak points
* no ingame help or hints if you are stuck with a particular puzzle. If you can't figure out the solution to a puzzle you'll have to use external resources like a guide. I got seriously stuck maybe 5-7 times during my playthrough, mostly towards the end as the puzzles solutions become more intricate. The game follows a mostly linear progression but with interim sections where sets of puzzles must be completed but the player gets to pick the order. On those sections there's typically some leeway so only 5/6 might be necessary to complete a particular world. An ingame help or guidance system of sort would have really been appreciated. In the Zelda series you'll meet with people giving off hints or even have a sidekick chiming in when you are stuck but there's no such thing here.
* inefficient solutions still work but are less satisfying: sometimes you might get stuck on a puzzle and find a time consuming way to meet the condition anyways. An example might best illustrate this. Consider a particular puzzle in which you need to crush a water creature in just the right spot so that its water flows into the grate below and fills some container. If you don't figure out the right way you might alternatively try to splash around water at different angles over and over in the hopes that eventually enough droplets end up in the container. That too solves the puzzle but it's certainly tedious and not satisfying. I've had multiple occasions where I eventually progressed but thought to myself Huh, that couldn't have been the correct way. There's no way to know after the fact though.
* upgrade system is largely useless. There's different unlockable upgrades in the form of nozzles that let you spray liquids at different rates or in different arcs and so forth but they're mostly gimmicks. Some actually do let you occasionally overcome obstacles in novel ways but the trick is that unless I tell you, you won't know which ones do that and which are useless. Upgrades are locked in permanently and cannot be swapped out. Nevertheless you can beat the entire game comfortably with just the default loadout. As a concomitant the exploration and secret hunting required to unlock the upgrades is also largely moot.
in summary
Overall, despite some frustrations, Vessel is a game that I'm glad that I dug it out of my library.
Steam Deck experience
Pretty much flawless. Haven't noticed any problems and the default keybindings work well enough.