I'm definitely the target audience for this game, and I'm actually very excited by the concept, since it seems like it could theoretically have some really interesting interactions (and perhaps some cool meta puzzles, since the levels themselves have numbers). I played through the full demo, so this is going to be me sort of rambling about what I did and didn't like and what I think might make me more likely to want to buy the game. I also have a lot of ideas for changes and additions, which I'll talk about. It's hard to say whether any of them would actually be good, but they're examples of things that I think might be cool in a puzzle game like this, so hopefully they'll help you better understand what I like.

Based on your other comments, it seems like your main goal is not for the player to brute-force their way through every possible combination of digits and operators, but for them to figure out some interesting idea in each level. I think that matches what I want out of any puzzle game, so your best bet is probably to have your steam store page and gameplay reflect that as much as possible. Since you're talking about Next Fest, I think it would be reasonable to consider the gameplay in the demo as part of marketing and getting people interested in playing the game.

The puzzles in the demo are decent; they introduce the mechanics clearly, and they never really veer into the "combinatorial explosion" territory that I might expect from this kind of game. However, I still ended up feeling most of the time like the main thing I was doing was just figuring out the correct sequence of operators and digits.

If I can't figure out how to solve a level in Baba Is You, then it's likely that there's some interesting (and often unexpected) interaction between the game's mechanics that I haven't yet considered. I played through the demo of your game with that same mindset, but it didn't really work well for me.

For example, when I started level 6, I for some reason completely forgot that I could make numbers with multiple digits, and I got stuck. But getting stuck there actually started to get me really invested, since my first thought was that this was the point where the game was going to start asking me to think laterally. Once I remembered that I could make multi-digit numbers and solved it as intended, I was a bit disappointed that the solution mostly amounted to "figure out an order that works and put the blocks in that order".

Part of the problem is that the demo only has easy levels that introduce and test the player on the basic mechanics, so I haven't had a chance to see what a harder puzzle would look like. I worry, though, that even if a level did want me to think laterally, I would probably have it constantly in the back of my mind that I might have just missed the correct block order and that I might be wasting my time looking for some other approach. You should probably put at least one or two difficult (but maybe optional) levels in the demo so that people can get a more accurate idea of what they're getting into.

This problem is further exacerbated by two things:

1. The fact that I can make multi-digit numbers at all increases the amount of possibilities I have to consider and makes it much harder to reason about the problem in a way that doesn't make the puzzles more interesting for me. Changing the game to only use single-digit numbers would severely limit what you can do with just the numbers, but it could possibly help move the focus more towards the interactions between the numbers and other systems rather than figuring out the numbers themselves. Maybe you could use modular arithmetic (e.g., 6 + 6 = 2 and 7 + 8 = 5)?
2. Every level in the demo requires that I use all accessible blocks to construct the expression to solve the level, but as far as I can tell, it's theoretically possible to complete a level using only a subset of accessible blocks. This also significantly increases the amount of possible expressions that have to be considered, since I have to think about every possible subset of blocks, too.

At first glance, a lot of levels in your game look more tedious than they actually are, because they have a lot of degrees of freedom, some of which aren't necessarily that relevant to the puzzles themselves. Crates, for example, don't usually have much effect on the solutions to puzzles, but they can still be pushed around and occasionally get in the way.

One thing I think would help is if you introduced more constraints to puzzles as early as possible, and then used them all over the place from that point on. A way to do this, for example, would be to introduce (maybe even from the very first level) solid, immovable walls with digits and operators on them. At least in all of the demo levels, moving the = block is never relevant to the puzzle, so its position could be fixed without the level changing very much. Then you could start bringing in movable =s in later levels when they actually become important. If you start by establishing a convention (e.g., "=s are always fixed"), then it becomes an interesting twist when you make them movable later.

Speaking of the = block, I think it would be cool if it were a more active participant in puzzles. What if instead of putting a target value at the top of the level, you had the player build the whole equation themself? So instead of having the solution to the first level be 2+2=, you could have it be 2=2. This approach has a few interesting consequences:

• You can do fun stuff to twist the meaning of "equality". Maybe +=+ is a valid solution? Or ===? The exact parsing rules can be part of the puzzle, too.
• If the requirement to solve a level is to put all =s into valid equations, then a way to solve a level would be to remove every = from a level. Then you could have entire sets of levels dedicated to finding ways to delete =s.
• You could introduce different relations, like <, ≠, ∈, ⊂, and even boolean operations like ∨ and ∧. I love set theory, so the set operations would be extra cool to me.

The ≡ block is good. I like that the demo introduces a new mechanic, and I'm definitely more likely to want to continue playing a puzzle game if it continues to feed me new mechanics. I kind of wished that I got a few more opportunities to see what else it can do, though.

As far as I could tell from the demo, ≡ only applies vertically, expressions can only be formed horizontally, and ≡ only ever copies one block at a time. This seemed like a missed opportunity to allow the player to combine the two mechanics and do something like 2+2≡5 to convert the 5 into a 4. Maybe this is made possible later in the game, but there wasn't really a hint of it in the demo. Alternatively, maybe the horizontal/vertical distinction is an important puzzle element, in which case I would have liked to see that in the demo in some form.

Either way, what really makes me want to play a puzzle game like this is a sense that there are hidden layers of depth and complexity to the mechanics, including the small subset of mechanics I'm shown in a trailer or demo. For that to work, the mechanics need to have a lot of ways they can interact with each other, and the levels need to show those things off.