I'd say Terraria is a great game. I'm not saying that because I'm on the Beta Team (which I am), but I think it's emulated on a popular game (Minecraft) but introduced its own elements to add to the uniqueness of the game. Because of this, Terraria has become quite successful and will probably remain successful for a good while. And unlike other games out there, the one thing that I've always loved with Terraria were free updates, as well as how inexpensive it is (especially with those huge Steam sales where it goes up to 75% off).
I love the game for it's large amount of content and playablility. I've played it since the very early alpha; I've been in the tester team from the beginning. It has a lot of nostalgic value to me by now.
I'll admit i'm a sucker for any game that has a craft & survive theme to it, but my god I love this game. Just for the sheer amount of content it has to offer and how it can be addicting at times. I was extatic when I first herd that it was being updated after so long.
I think this game is a lot better than minecraft (besides the 2D and 3D graphics), and it has a huge variety of bosses and items that makes this game completely endless.
I was almost a tester in the beginning, so in terms of that I've played since its first release. I was greatly marveled at the sight of the game; the atmosphere, the design, the gameplay. Sure there were bugs along the way, but it seemed flawless regardless of the fact. Then what seemed to be a small project became a big success. The world of terraria before me had completely changed as hardmode made the game utterly mythical and phenomenal. Even through its temporary downfall, I played for hours on end wanting to acknowledge the distance the game had gone in only a year's time. Lucky for us, the game returned, and content we have never seen so large before crashed over us. By this time terraria had become more than just "a minecraft-esc game". Why do we love terraria? There are possibilities are endless.
It's a wonderful game. Haven't played it since the Halloween Update, because I haven't been able to play with my friends on multiplayer since then. I really should get back to it though, since I've missed out on what seems like a lot of new content.