As you explore and find minerals and other items, you'll be able to craft more than 200 different things, from tools and weapons your character can use to chandeliers and bookcases for decorating your home base. Check out the crafting recipe page at Terraria Wiki to see the types of things you can make. If you haven't guessed already, this is a game with a immense amount of depth (pun intended), so if you were looking for a simple casual distraction, this is not the game for you.
The controls are not perfect
The touch-screen controls are functional, but not ideal. To move your character, there's a control pad in the lower left of the screen. Any item you use, whether it's a sword or a blaster or a stick of dynamite, is activated by touching the right side of the screen. Where in the PC version of the game you mine by pointing your mouse cursor at a block and clicking, with the iOS version you just touch the block with your finger. This opens up a small zoom window so you can see exactly which block you're mining. On the iPad, this control setup works fairly well, but it still can't compare to a keyboard and a mouse or a game controller. But when it comes to the smaller screen of the iPhone or iPod Touch, it's much more frustrating.
The difference between the two devices is more than just a difference in screen size. With the smaller screen, you actually can't see as much of your surroundings at one time as you can on the iPad. But to make it even more frustrating, the small zoom window will actually sometimes appear halfway off the screen so you can't see which block you're mining. Hopefully, a fix will come in the next update that smartly pushes the zoom window below your finger when it's getting close to the top of the screen, but iPhone and iPod users should beware of this limitation before buying.
Terraria for iOS stays faithful to the original with the same graphics, enormous open-world maps, and hours of fun gameplay. The touch-screen controls are a little tough to get used to and not as good as a mouse or controller, but are mostly functional on the iPad. On the iPhone or iPod Touch, not as much of the map is shown, and the zoom window sometimes goes off screen making it difficult to recommend for those devices.
Still, whether you have played Terraria before or are new to the game, the iOS version is an excellent port and makes for the perfect time killer as you explore an enormous world and battle challenging bosses. But until an update fixes the small screen problems, I can only recommend it for iPad.