Oh man, Crystal Project. I had a really weird engagement arc with this game!
For whatever reason, I was really determined not to give this game the time of day at first. I found the trailer videos on the Steam page absolutely repellant, for some reason. I don't know what it was, but something about the voxels and the floaty physics just rubbed me extremely wrong, so when it was first recommended to me I took one look and then decided it wasn't for me. And then someone else recommended it to me. And then someone else again. And finally it hit critical mass, and the demo was apparently giant, so I said "fuck it" and tried it anyway, and ended up basically 100%-ing on Hard mode and playing it for over 120 hours.
I'll say that I'm not sure that the game does a good job communicating what it is, but that's because what it is is pretty unique! It wears the skin of a survival crafting game (which I generally don't care for), but it is absolutely not one. Fortunately, if you're someone who, like me, isn't sure that you'll like it, the first thing to recommend it is that aforementioned demo-- I think it may be the most generous demo that I've ever encountered? I played the demo version for over 15 hours, and in those 15 hours I only found a single pay-wall, and I had to go well off the beaten track to find it. And then you can just seamlessly load up your demo save into the full game and you're off to the races (this is a joke for the Crystal Project heads).
Loki did a great job above describing what makes this game special, but I'd still like to dive deep on some of the game's core systems.
First off, and this isn't a comparison that I saw other people make, but I think that the game this reminds me most of is actually Alundra (not the combat, obviously, but the platforming). A lot of trying to judge heights and differences in 2D to make jumps. Perhaps also shades of the platforming/puzzle-solving of CrossCode's outdoor areas, to cite a more recent example. And that platforming is in service of exploration that is extremely rewarding. There's always a new secret hiding just around the corner or out of sight. It has DQ-style "you need to build this bridge to proceed" checkpoints, except that almost all of them can be circumvented if you're thorough and clever and want to go mash your face against enemies that you're not ready for yet.
The combat and class systems are also aces. Character-building has shades of FFV. Each class has a skill tree that it earns job points for, and each character can have a primary and secondary class skill set at any one time, but can equip any passive unlocked from any previous class (up to a point-- there's a passive capacity). Stat-ups are decided by the class you inhabit at level-up, but you can re-spec those class-ups for money later if you're unhappy with a build. Also, characters earn job points at 1/10 rate for being around other characters in that class (just one of many small clever touches this game has).
Combat has an AP resource that builds-up over time and resets between battles, so you can use your abilities as much as you like. It also introduces MMO-style threat management into its turn-based battles and it works super well! Rogues can only backstab if they're at the bottom of an enemy's threat list. Healing generates threat against whichever enemies are targeting the party member you healed. My party had a tank with taunt and cover abilities. One of my favourite strats was having my Wizard open up with a big fuck-off AoE, then having my Tank use Cover on him with a counter-attack passive. I've never seen anything quite like it before, but it all just works, and is rather intuitive to boot.
As I mentioned, I played Hard mode the whole way and can say that it was just perfect for me, and the end game super bosses, of which there were many (some of which can be found quite early), had teeth. The end/post-game content reminded me a bit of FFIV Free Enterprise, the FFIV randomizer, of all things, in the way that I'd try a boss, decide I didn't have the right kit, then go find another one in hopes of having better kit later.
Anyway, I'm glad everyone kept recommending this one to me, because it's a GOAT. Give it a try right now, for free!