A subversive platformer in the vein of Super Mario Bros. and a pleasurable discomfort as you work deeper into the world.
Eversion is a platformer in the vein of Super Mario Bros. (to the point that the game files call the enemies "goombas", and an achievement makes reference to the first SMB). On the subject of Achievements, those, leaderboards for a "time attack" mode, and graphical improvements are what you're actually paying for in this Steam release; the developer, Zaratustra Productions, also has a freeware version available at their site, zarat.us/tra.
According to the manual (available from the game's Steam Store page), you are Zee Tee, a brave -a-s-t-e-r-i-s-k- warrior, out to save the Flower Kingdom's Princess -N-e-h-e-m-a-, -k-i-d-n-a-p-p-e-d- by the Ghuliba forces of the north. Aside from that, there's not much explicit story to be had. However, as per the game's title, there are many layers to this quaint little story, just as there are layers to the world itself. Along with the jumping around, jumping on enemies, jumping to headbutt blocks established with SMB and its kin, the eversion mechanic allows you to evert at certain places on the stages, changing how the stage behaves. The physics will always stay the same, but stage elements and enemies will shift with the peeling layers of reality.
And you'll need to evert, too, to get everything there is. There are 240 gems to collect, and nabbing all these buggers will push your reflexes and understanding of the game's mechanics to get yourself to where they are. There tend to be at least a couple ways to accomplish these feats, though, which opens it up a bit for experimentation.
I definitely like the graphics boost this version has over the freeware. The added detail really brings out what you're seeing, and keeps it from becoming "just a bunch of sprite tiles". The only sacrifice is one if you prefer simplicity, especially during the endings (oh, yes, there's more than one ending to find), but I don't think the little flourishes diminish the effect the game gives. The music helps with the effect, though it may get on your nerves if you end up in a stage too long. However, until that point, they're pretty catchy, with a technical level that matches the retro aesthetic the game's made with. And both will help you find the eversion points, as these nexuses will blend the sounds and colors of the layers they lead to.
As for the challenge, I think you'd have to know if you're compatible with platformers to play this one. If you're cool with the run-&-jump, you should be able to get through to an ending with enough effort, though to truly delve into everything, you may end up offput, but not enough to drive you away from the game permanently. The levels, aside from the first, have checkpoints midway through the stage, though if you quit the stage, you'll have to begin from the top. Some stages require precise jumping (with one calling for vertical block-scaling, jumping from one block to one directly above it) or races against time, and compiled with the other stage dangers, you can end up falling to your quick death many times (each time resetting the music, to boot). The game's not too terribly long, though, at less than ten stages (with a couple as part of the Time Attack mode), so if you're especially good at platformers, you may end up breezing through. And for any skill level, have some solace that your gems (and hidden 'items'; one per stage) are saved as soon as you grab them, so if you die, you don't lose your loot.
Despite how much time you get out of it, at five dollars, it's not a bank-buster, and I like what the game does to recommend it to anyone willing, whether they go with the freeware or Steam release (though if you're letting a friend play on your account, you may want to move your .sav file somewhere else and let them have a fresh start). It won't warp your brain, but it can make you uncomfortable/insecure in the game's world, and for whatever frustrations it gives, I did have a smile on when calling out on the game's ridiculous "bullcrap" moments.
Just, just keep in mind: this is "not suitable for children or those of a nervous disposition." *wink*
NOTE: My Steam profile reads me as having 11 hours on this game, but some amount of that time was just goofing around or showing it to my folks (because, really, it's that neat).