My $10 were NOT wasted
Terraria doesn't need great graphics, a great soundtrack (though I do like the background music in different areas a lot), or a story. You decide how fast or slow you go through the game. You can build many things in Terraria which are only limited by the fact there are no cheats (that I'm aware of, anyway) and have to gather your own.
Exploring your world, gathering resources, building whatever you want, becoming stronger/better and lots of digging is what this game is about. I've enjoyed my experience with it greatly and I am very glad that my friend forced me to buy it so we could play Multiplayer.
As for Minecraft, if you like it and aren't sure about Terraria, give it a try and vice versa. They have similarities, yes, but they are by no means "the same game".