I like them both, for similar as they are, they succeed in different ways. Minecraft is much better for building impressive structures, but Terraria has a much broader range of content better combat. Yeah, I'll take both, please.
As for your other question, I can't say for sure that this will usher in an entirely new genre that will leave its mark on the industry forever, but I'll bet you an oreo that there will be many more similar games, yet. In fact, I'd say there's a pretty good chance of a big-name studio with the funding of a publisher taking a crack at it. I hope they do; I'd love to see what they would do with a couple millions in funding AND and opportunity to learn from the strengths and shortcomings of two successful games like it.
As for your other question, I can't say for sure that this will usher in an entirely new genre that will leave its mark on the industry forever, but I'll bet you an oreo that there will be many more similar games, yet. In fact, I'd say there's a pretty good chance of a big-name studio with the funding of a publisher taking a crack at it. I hope they do; I'd love to see what they would do with a couple millions in funding AND and opportunity to learn from the strengths and shortcomings of two successful games like it.