Terraria is a sandbox/adventure game released on May 22, 2011. It was developed by ReLogic and published by 505 Games.
The core gameplay elements revolve around exploring, crafting, building, crafting and mining, similar gameplay elements to Minecraft (However not at all a copy of it).
I have a soft spot for Terraria, as I've played it since I was young on my grandfather's iPad. It was the first game I bought on steam, and probably the first game I put more than 100 hours into. Knowing this you might guess that the review will be biased, but I will try my best to state fairly the game's strengths and flaws.
Now keep in mind that a new update to Terraria is getting released very soon, so my opinion may completely change when that releases (definitely for the better).
Getting into it, Terraria, at it's core, is fun. It's fun to play by yourself, it's fun to play with friends and it's fun to play in a public server (though they don't run the best), I can tell you this much.
People may be deterred by the graphics (which I have grown to love), but if you're not playing games for their gameplay, why even play them at all?
The other big turn off is that the game is 2D, however I think that the fact that it is 2D greatly benefits its core gameplay and mechanics, and I definitely don't think that it would work as a 3D game, or at least to the degree of it in its current state.
Terraria is a sandbox boss-rush with heaps of content and a style that doesn't take itself too seriously. You run round, gather resources, craft stuff and then fight a boss on the huge roster of them. Simple, but effective.
There is progression, you can't just fight bosses willy-nilly, and once you beat a specific boss (called the Wall of Flesh, or WoF for short) you will enter the game's second stage, called Hardmode.
This isn't fighting all of the bosses again with slightly harder stats, this is the second half of the game, with heaps of new interesting items, enemies, bosses and biomes.
Certain bosses (such as the final boss, the Moon Lord) require lengthy processes to even START fighting them.
All this may seem overwhelming and daunting, but the fact that it's a sandbox game means that you can tackle it at your own pace and do things in your own order.
(Didn't have time to finish the review)