I bought it and had 20h+ of fun with friends. The game ran out of content pretty fast though, as I got the best gear and had no trouble killing any of the bosses anymore.
I haven't tested out the latest added content though. IMO Minecraft is still way better, but Terraria was a fresh new thing with a twist of Minecraft in it. Fighting-wise Terraria is better, but it's the crafting and building that makes motivation for Minecraft last way longer. In a 2D-world the things you can build are much more simple anyway, although I did see some funny looking stuff (pixel art, biodomes etc) that people built in Terraria.
You can find me from the CCGR Steam-group, feel free to add me as a friend!