There isn't much info just yet, but check out this video so long:
This is the description from their website:
Set in an alternate dimension within the Terraria universe, Terraria: Otherworld places the player in a life-and-death struggle to restore a once-pristine world – now overrun by a malevolent force that has corrupted nature itself – to its original splendor.
Combining elements of sandbox gameplay with role-playing and strategy elements, Terraria: Otherworld explores the Terraria experience in an innovative and unique way - providing a fresh approach to the “open world” genre.And here's the link to the official Terraria Otherworld site
Is it weird that a game like this excites me much more than any AAA title out there?