Terraria is a 2D sandbox survival adventure game. The gameplay consists of exploring a randomly generated world while building structures and farming resources for said structures as well as equipment and weapons. A survival game at heart with a sandbox base.
While there is little to show progress in the game over gaining many items and having many structures built, progress overall can be slow due to having to collect every item needed to craft the necessary tool, equipment and materials. This can be time consuming and may turn some people off.
Instead of building a deliberate feeling of suspense, Terraria uses bright palettes and arcade action to provide a fun experience outside of the survival elements. When those elements gradually appear one by one, each is all the more shocking from the contrast.
Terraria has a very large community as it is a very popular game. Released on just about every platform including mobile, PC/Mac/Linux, consoles, it allows for anyone to play no matter their prefered device. This also means that with many players comes many servers to play on as well as tutorials...
Starbound allows the player to go at their own pace while completing the tutorials. By the end of the tutorials the player will have the skills and equipment to succeed in the game and have fun doing it.