I've played this game since I was a kid! I chose Terraria over getting Minecraft growing up... and I still favor it over Minecraft. They're not really comparable as games, even though people who don't play Terraria refers to it as "2D Minecraft."
Terraria is a sidescrolling sandbox building game, where you create these realms you have to protect, fighting a series of bosses.
There are different types of villagers you can unlock and have them move in as residents, and there is a blight of the land called the "Corruption" or the "Crimson" depending on the realm, that spreads and corrupts the land.
You have to find a way to prevent it's spread and to cure it.
Theres thousands of items to discover, and there's a whole other mode of the game with thousands more to unlock after defeating the final boss of Softcore Mode.
My realm is called Ozomel.
Ozomel is corrupted by The Crimson and The Hallow.