This game is deceptively complex!
In addition to crafting, digging, mining, and building, there are also a surprising amount of RPG elements to the game, such as as gear and complex weaponry, vendors you can attract, and bosses you can kill. In addition, the multi-tiered zones of depth that you encounter as you venture underground hold a lot of surprising variety in enemies and randomly-generated caverns and mineral veins.
The same goes for the various surface biomes that you will come across. While you start in a pretty generic forest, you can encounter snow, desert, jungle, ocean, corruption (demon-infested lands), and other wondrous realms. The enemy variety (and hence the difficulty difference) between zones is substantial, as is the variety of materials you can use for crafting.
The aesthetics of this game lend themselves to the general ambiance of exploration underground quite nicely. The gentle flicker of blinkroot briefly illuminates the silhouettes of enemies, chests, or other mysterious objects in neighboring caverns, enticing you to dig deeper, and the first time you encounter giant glowing mushrooms is really a treat.
The soundtrack is superb, alternating based on the area you are in, both in depth and latitude, and the old-school graphics are refreshing.
Overall, the game is highly addictive, and very fun with friends.
I have only a few criticisms. First, being an indie game, this game has no real tutorials, and it could really use some. While the initial mechanics are pretty easy to understand, the interface is not particularly intuitive, and some of the more complex game mechanics may escape your notice entirely even after playing the game for tens of hours. It basically forces you to look things up in the wiki.
In addition, crafting recipes (available through the hint/tutorial NPC) should really just pop up at the appropriate station whenever you have picked up all the ingredients at some point. it's often unnecessarily troublesome to learn what you can create with your mined goods, and using what platform.
Finally, it is needlessly difficult to play with other players. There is no server browser, even though the only way to play with others is to join a player's server (there are no official ones) and you MUST do so by entering the IP of the player. There should at least be a basic browser where you can see people who are hosting and a few details about their games.
Generally though, the game is really quite fun. I wouldn't miss it if you have any sort of creative inclination.