Terraria was just released in the U.S Appstore just a few hours ago. The game is $4.99 and is an exact PC port with all the features the PC version had.
The game works extremely well with touch controls, so far there hasn't been an issue. One thing 505 Games could add would be the option to change sizes of the joysticks.
Go get this game if you are a fan of the PC port or even a fan of minecraft. Android and windows phone versions are coming "soon".
Terraria ios is out now