I've played Starbound and frankly it was extremely boring, because there wasn't that much to do.
Is Terraria any better?
It's a complete game, so yes.
As you play the game there are generally some set goals for you to do (which you don't have to), which include gathering resources to get next-tier items, visiting the different biomes, defeating the pre-hardmode bosses (there are 3), exploring the dungeon, exploring the jungle, finding sky-islands, getting to the bottom of the map and the underworld, fighting the Wall of Flesh (the hardest pre-hardmode boss in tricky terrain), entering Hard Mode as a result, getting brand new resources and tier items, fighting new bosses and new enemies, defeating Plantera, a hardmode boss who opens up the final part of the game, exploring the Jungle Temple, fighting the boss there.
Then after that you're probably at the end of a normal exploration run.
But you can fight more bosses, different monsters in different biomes, there are random events, like goblin or pirate invasions, and then there are Pumpkin/Frost moon events, which you trigger, and start a full-scale invasion of enemies with unique powerful bosses who attack in waves, earning you special loot.
Then you also have the option of playing with friends, joining servers with other players, creating cool houses/bases, gathering all the NPCs, playing PvP with other players (including a CTF gametype).
There is a lot to do.