Too bad terraria is stuff.
It's not stuff, it's got plenty of good stuff in it.
It's also like 4 months in development, although the developers dun goof'd and decided to release it early.
I've only played Terraria for a day now, but this quote from a Minecraft modder sums up my opinion of the game nicely:
I also started playing Terraria after I played Minecraft, and saying that you could blow go through Minecraft's content just as fast isn't true. Minecraft could learn a lot from this game, it has a much more diverse selection of items and monsters. But I've played Minecraft for months, and after a few days I'm already getting bored of Terraria. I think it's because the building aspect of Minecraft is so much better. It's more fun in 3D and the blocks are bigger so it seems less tedious (especially with having to hammer out dirt walls). I don't know what it is but Terraria just doesn't pull me in the same way. I think the map size has something to do with it as well, I created a large map and I've explored the whole surface, it's not the same as the epicness of Minecraft's infinite maps.
I also think that having a character all your items are saved to doesn't help. When you go to a new server or start a new map you already have all the best gear so what is there to do? The fact is you can build much grander things in Minecraft much easier, and things like redstone add to the fun. The building is what keeps you playing, not the monsters. Terraria has a lot more to offer in terms of monsters but Minecraft has a lot more to offer in terms of building, and that just lasts longer.
Therefore, once Minecraft has a bit more focus on survival and adventure (AKA the next update!) it will be much better.