Positives:
-Fast progression system up to the endgame.
-Scary atmosphere.
-Even though mining is the main way to progress through the game, killing enemies does give ores and ingots.
-Your jumping height is like three blocks, and you can double jump, making cave exploration easier.
-Sound design for most enemies makes them terrifying.
-Wide variety of guns to use, with the shotgun being the best and most fun to use.
-Enemies are always challenging.
-Tools do good amounts of damage, so you don't need to completely rely on swords and guns.

Negatives:
-Endgame content revolves around finding a very rare biome and mining for several minutes while endless enemies that two shot you repeatedly spawn.
-Even though the game is centralized around exploring, the sprinting bar runs out in less than two seconds and takes four seconds to recharge.
-Armor doesn't exist, so you constantly have to deal with enemies three-two hitting you.
-Enemies lunge at you from insane distances.
-Every time you're too close to an enemy, your character either moves way too slowly or just completely stops moving.
-Dragons always spawn once you go far away enough, and they follow you FOREVER.
-Enemy spawn rate is way too high, even during the day.
-Once you've obtained the best weapons and pickaxe, there's literally no reason to keep playing since there's nothing else to do.
-Melee weapons break too quickly and are awful.
-There's very little building blocks that you can craft.
-Hell biome is just filled with hordes of enemies that spawn right next to you and from above.
-Endgame gear requires you to find the same very rare biome to replace gear and refill on ammo.

Summary: It's only fun for like a day, but after that it just becomes either boring or tedious.