Next Fest is close and your demo is probably not enough
Most of the demos you play on Steam are not actually demos. They are prototypes. Most developers use the demo system to put the game in front of players for the first time, so as a kind of free R&D and QA. But it is the wrong channel. A demo is a marketing tool, betas are a development tool. The player who plays your game in its bad state in a beta and tells you where he got stuck is doing you a big favour. But the moment you put up a demo that relationship turns around, now you want wishlists and visibility, so you are claiming you already know the game is fun.
People always go to the same place when they hear this. “I put up a demo and collect feedback too, the two are the same thing.” They are not. Dome Keeper did this right. The game was a 72 hour jam piece on itch under the name Dome Romantik, it came ninth in Ludum Dare, and the Steam decision came after that answer. The itch version was a week of work, the version that went to Steam took years. The same build cannot do both, because the two do different jobs. A prototype asks “can this be a game”, a demo asks “will you buy this game”.
What the player is really waiting for when he opens a demo is a vertical slice. Think of your game as a timeline stretching from the first minute to the hundredth hour, a vertical slice cuts that line vertically and takes a piece out. Maybe 5% of the game, but at final quality, so the person playing feels what the finished game is going to be like. Most developers think this is only something you show a publisher or an investor, but your real investors are your players.
One of the biggest mistakes indies make is taking the first tutorial section and putting it up as the demo, where the rest of the systems are visible in the UI but none of them are playable. For example you collect plenty of items through the tutorial and they all go into an inventory. There is also a magic system sitting in the UI. But the demo is so narrow that none of it is ever seen working, you see that the inventory is there and you do not use a single thing inside it. Two unanswered questions are left, how does this system work and what is in the rest of the game. Because you cannot play it you cannot decide whether the game is for you, which was exactly why you opened the demo. The player does not read this as mystery, he reads it as being tricked. Someone burned by early access in particular reads it as “these systems do not exist yet”, and he is not wrong.
If your demo is the first section of the game, it has to contain what the game is, completely. If your game has both shooting and base building and base building opens up in the middle of the game, when you do not put it in the demo you have not explained the game. The thing you think you are hiding has actually never been communicated to the player. And for you to find your own audience and convince them, however many features set the game apart, they have to be in the demo. There is an example done right as well, the We Harvest Shadows demo is quite long and plays the cozy and horror mix all the way through, and the player comes out knowing exactly what he is getting.
None of this leads to every game having to ship an hour long demo, because in some genres a vertical slice does not explain the game at all. In a city building game you have not built a city in thirty minutes, the demo ends before the player can construct anything. In management games, in 4X, in survival and crafting, a person plays a single four or five hour session and only understands the game at the end of that session. When you compress a game like that into half an hour you have shown the player the menus, not the game.
The solution for these genres is called a horizontal slice. Here, instead of taking a vertical slice out of the timeline, you give all of the game’s systems but you cut content. The player plays one full session from start to finish, touches all the core systems, and only does not see the later content of those systems. In an RTS you let them play one faction, in a survival you leave two tech trees out entirely, in a city builder you keep the late buildings locked. Prison Architect went into early access exactly like this, there was only a sandbox mode and no campaign.
And this is exactly where it differs from only giving a tutorial. There the system has a name but not a body, here all the systems are playable and it is said openly that what is missing is content. The player forgives missing content, he does not forgive a missing system.
The question to ask while designing the demo is why someone who likes the idea of your game would hesitate. In a cozy game, is it too empty. In a roguelike, are all the runs the same. In a city builder, is it deep enough. Once you have found the answer, put the thing that closes that hesitation right in the middle of the demo. If you are making a roguelike, let the second run be visibly different from the first, if you are making a city builder, let the player get stuck once inside the demo and solve that himself. Hiding features does not earn you mystery, it just leaves that question unanswered.
A demo is not a slice of the finished game, it is a promise of how it will look when it is finished. And while you are making that promise, every system you cannot show becomes a system that does not exist in the player’s head.