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.
Pro 2D retro-platformer style
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.
Pro Encourages creativity for all ages
Terraria is like a 2D Minecraft, so you can alter the world around you and craft things, which teaches creativity and critical thinking skills. This is great for children who enjoy building and discovering new ways to tackle ideas just as it is great for adults who enjoy the same things. It also makes for a great objectiveless game where you can do just about anything you want, which allows for less stress due to being able to play at any pace the player likes.
Pro Multiplayer with up to 8 player online co-op
Up to 8 online players can be invited to join a shared Terraria world, including worlds that are also used in single-player mode. This allows for large co-op or PvP games to be played, for those that are interested, meaning you can choose how you play. Build something big together, or destroy the other guy's base.
Pro Large community
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 and Let's Plays. So finding content or help or just basic information on the game will be quite easy.
Con Gameplay can feel slow
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.