Released in the same IF Comp as the much better-known Rameses but nearly universally reviled, this overlooked experiment also casts you in the role of a player unable to make your character do what you want, although this time with much more disturbing consequences. A story about a serial killer who rapes, disfigured, and murders his female victims is perhaps not well suited to the second person voice: the graphic violence and nihilistic themes make this a challenging story to complete. But there's more going on here than shock for shock's sake.
As with Rameses, your commands are often rejected or ignored by your character, whose insatiable and growing desire to commit heinous acts of violence becomes increasingly strong as the story goes on. The player is essentially cast as a desperate super-ego totally powerless in the face of a raging, terrible id. In the first segment, you can explore a small map at will, and take actions other than those leading to murder, but later, any direction you move in takes you closer to your next victim, and any attempt to escape your situation or alter what you know to be coming is rejected, even to the point of innocuous commands being eagerly understood as hurtful in intent. Descriptions are sparse and default messages brief, focusing on your victims to the exclusion of all other details: often nothing is even implemented in the world model but your victim. When you give in to your compulsion, only then does the screen erupt in pages of text, recounting the result in gruesome detail.
You also play the killer's psychiatrist and the chief investigator following the murders, and both characters are portrayed as equally railroaded and impotent. As the middle-aged woman in charge of the investigation, you must engage a misogynistic coroner in conversation even though you despise him; the psychiatrist is forced by professional code into morally ambiguous position(Spoiler - click to show) (though he's revealed at the end to be another personality of the killer, this personality doesn't seem to know about his alter ego). The implication is that these characters must play their roles in the same way the killer does: the investigator is unwilling or unable to shirk her professional duties, just as the killer can't stop killing.
The game is merciless in reducing the agency of the player even further wherever it can. Abrupt transitions between segments often immediately follow a command, before the response is printed, creating confusion and helplessness; exits are universally omitted from room descriptions with similar effect. Likewise, the available topics in the conversation system are obscured, and only discernable through annoying suggestions from the other characters, meaning you can only engage with them on their terms, not your own. All these factors add to the sense of impotence in the face of the unfolding events, and connect the gameplay aspects even down to the level of parser with the themes of the story.
Even if you're willing to buy into this meta-gameplay, 1-2-3 has problems, including a predictable plot twist and some less-polished writing in its second half, and many people will be understandably turned off by the subject matter alone. More than the graphic violence, though, the game disturbs because of its unflinching look into the minds of people who feel helpless to alter the course of their lives. It's not a lot of fun to play this game, but that's probably the point.