I think it is a fun little reminder of lambda calculus principles. But I can't recommend it. The issue just comes down to a lack of polish I'd expect for a paid game.
The most glaring issue is inaccessibility. The game has a minimalist, terminal aesthetic - that itself is fine, it fits the point of the game. But it is very hard to read the text - it has a small, blocky font that is unpleasant to look at and difficult to read for users with worse eyesight. There are no settings to customize this, no accessible mode. Font size and style should be the minimum required settings for a terminal game like this. Instead you just have a volume setting.
The controls are also a bit of an issue. The game seems to use an odd mix of keyboard and mouse controls. There are some buttons that can only be clicked, like solution selection, or 'open on playground' button, but don't seem to have key controls. On the other hand, menu items aren't buttons and can't be clicked; you have to navigate using keyboard only. So you can use keyboard for most things, but not all, and still need a mouse, but you can't use a mouse everywhere you'd expect. I get it's trying to be a terminal game, but it just doesn't have the consistency one would expect.
This really is a refresher for lambda calculus. It's not an introduction. And unfortunately that makes it less of a game - it's geared towards people who already know the content well, not those looking to learn something new. I think the endearing thing about the Zachtronics games is that you don't need the exact technical background to get into the games - it might help, but it's not necessary. The games build from zero, and have the necessary documentation and explanation to introduce even beginners to the material as you go. This game just doesn't have that.
The first level, 'anything', is fine enough. It gives you a few example terms, and you just copy one. But starting from the second level, 'identity', things break down. The game freely mixes formal notation and in game syntax, making it difficult for the player to separate them at first. In the info boxes you have formal syntax like '->' and 'A[x=B]' which are used for explanation but don't relate to the actual syntax you use as a player. I spent a bit of time wondering if it was possible to label my own functions for reuse (it is not). You slowly build up a set of functions you can reuse in later levels, but there's not any document to describe or explain things aside from the info boxes in each level, so if you need to look something up, you need to go back to the individual level. The info boxes do help a bit, but just don't feel like they are written for someone who doesn't already know lambda calculus.
Finally, at least on windows, there is an open terminal in the background with debug info as the game runs. As a player I'd prefer if... there weren't?
