For a game that prompts you to mine far into the earth, it seems shallow.
Just going to state right off the bat, the graphics are pleasant, but the repetitive music gets on the nerves after a while.
Now this game is a ton of fun at first, especially when you start to dig into the earth and search for more and more tools and fight more and more monsters. Seeing the different hazards you need to bypass underground like water and finding ways to move past them, and use them to your advantage is also a joy. Problem is it gets old, and the extra upgrades and repetitive monsters, really aren't worth finding and fighting, unless you feel the need to construct that huge city or castle in the sky which ... is made for only one person and your small group of NPCs. It's nice to look at, but I can't help but feel all these achievements are like an empty shell. This is because of the complete solitude you feel in the game. Your NPCs are boring and assist you in basically buying and selling. Terraria unfortunately, though it does have amazing settings and places and monsters, seems lifeless after you see it all.
Multiplayer can be pretty cool, especially when you have a digging partner. But even then, what you both or your group will have to do in the game, is limited. You don't have to fight monsters if you don't want to, and there isn't a challenge in protecting anything you've built, like your community. And it's a complete pain when the random buddy you find has basically all the best weapons and can simply toss them to you.
I do like Terraria, it's fun to mess around with and it's cool to build your first house and build your first mine. It's unique and the battles are solid. But after that, the second go, it all feels like a waste of time.