Initially, after playing this game, I immediately wrote a review on Steam that consisted of me (who was, at the time, soaking my own shirt in tears) talking about how much of a tearjerker the true ending was. By that alone, you should certainly be able to tell where this much more proper review is heading.
Oneshot is an absolutely fantastic game that is so much more than what it appears to be on the surface. The protag of the game, Niko, is a great bundle of fun with a very endearing design and a hilariously innocent and emotionally honest personality that any person can easily grow attached to within mere minutes. While the cast of the game is small, as is the run time (something that will be spoken about later), each character is very likable and definitely memorable, even the minor ones, such as one of the female characters you meet in the Cafe of the game that offers Niko food.
The game is aesthetically beautiful, the most notable example being The Refuge (the last section of the game) where different shades of red all shine to make a filled up bowl of eye-candy. All the colors blend in really nicely together; I could really look at some of the parts of this game forever if I wished to. You'll also get semi-frequent cutscenes throughout the game which let you take a closer, more detailed look at what's going on.
Whilst the game is a very simple pixely mesh of graphics, I don't think it at all takes away from the overall experience. Sometimes simplicity is better, yeah?
The overall idea of the game is that Niko, who wakes up in an old, abandoned looking house, is destined to be the Messiah who restores the decaying world's light with a lightbulb he finds in the aforementioned house which just-so happens to be the sun of the world. Whilst, at the climax of the game, you do have the option to restore the sun to the Tower of the game, it will also trap Niko in the world, allowing him no escape. You also have the option to smash the sun which will instead leave the world to die, letting all the other characters perish, then allowing Niko to go home. It's the definition of selfishness vs selflessness and a pretty decent way of tugging at the heartstrings.
Once you meet Prophetbot, a minor character who was built specifically to talk to Niko upon his entrance to the world, he also tells Niko that you, the player, are their God, meant to safely guide Niko as he travels along. This is where the fourth-wall breaking comes into play, something the game uses as a main feature. To elaborate, many times, what appears to be the closest thing to an antagonist of the game, the World Machine, will mess around in your documents folder alongside your general computer. You'll usually need to search around and find secrets hidden in your folders and what not to progress through the game. This makes for a very unique and interesting experience, one which I haven't really felt with another game before.
There's a very nice selection selection of music in here as well! They really work with the atmosphere of the game and are very nice to listen to. Each track really fits with where it's placed in the game and each one is extremely memorable.

SPOILERS AHEAD
Just the initial playthrough is solid, but, where things really shine (no pun intended) is the Solstice ending. This ending is achieved after you delete your save data after the first run and restart the game, causing a new option to appear upon the title screen. After inserting the password, you get to start the Solstice route, where things become different as soon as you hit the mines.
In this run, the world slowly starts to be corrupted by squares; the main objective going on to turn from restoring the world with light to restoring the world from total corruption as Niko learns from special characters restricted to this run that he exists within a game and the program (the World Machine) is trying to kill itself due to the first law of robotics which states that a robot may not put a real, living person within harm's way. Alongside that, you learn most of the actual lore in this playthrough of the game, which is essentially, the "author" created the World Machine (aka the game) to replicate the dying world he had suffered within. As said, because of the violation of the laws of robotics, the World Machine turns chaotic and attempts to kill itself and tries to force Niko to smash the sun, which would cause him to return home, to the real world, and leave all the other characters (who are supposedly just code) behind.
In the final part of Solstice, Niko confronts the World Machine, who uses Niko's reflection to communicate with him. I really don't want to talk about this part in great detail, just because I feel I couldn't explain with words how truly good it is. It really is a tearjerker and one that is much better having seen or played than reading.
But, to try and summarize, Niko eventually convinces the World Machine to recover the true ending of the game that had been long gone after accidental corruption of the code- said ending being Niko getting to go home after making the final decision with the sun. Eventually, the World Machine succeeds in recalling the ending, letting Niko finally be able to go home and leave the world you and him had experienced. He says his final goodbye and leaves for good, the journey finally ending.

The one minor kink people seem to have with this game is that it's a tad short - Taking a few hours if you know what you're doing. This is certainly a fair criticism and I think I can agree to it - While I have heavy praise for the game, I feel if it was given just a bit more time, a few more hours of areas and characters to expand upon and grow with, it could have been even more fantastic.
Overall, I think Oneshot is a beautiful, heartbreaking and adorable game. If you want a really damn solid RPG Maker game and have a few bucks to spend, Oneshot will be waiting for you. It's such an engaging, appealing game, and, despite its length, it'll be one you wont forget. Guaranteed.