We're definitely aware of Terraria, and it's something Keith has played a fair bit; he brought it to my attention when we were just getting started on AVWW and I made a certain suggestion, actually. I haven't played it, but I've played loads of Minecraft, which I understand has something of a similar interface in some ways, and even in the past versions I think you can see a bit of a Minecraft influence in things like the ability bar, etc (though Neverwinter Nights, which I also enjoyed, plus a number of dungeon crawlers that Keith enjoyed, could just as easily be said to be the inspiration).
At any rate, one of the things coming up in the reveal is a revamped UI in a lot of ways, although I'm not sure if we'll actually have the menus at the point we want to show them, yet. But we've gone through not one but two conceptual overhauls of our GUI in the last couple of weeks. The result is something that is super, super streamlined but also really powerful; even moreso than Minecraft, in our opinion, although obviously the games are very different in focus in the first place, so that's not even a knock against MC. Our inspirations for the final designs came from diverse places such as what we already had, Minecraft, Torchlight, Neverwinter Nights, and a few others.
Our primary goal was to have the least-possible amount of clicking and fiddling with anything so that you can just play, and our second goal was to make it so that you wouldn't need to run back to settlements all the time to store your stuff because of super-limited inventory.
Anyway, that's a pretty safe topic, and it's one of the more minor things that is changing at the moment; minor mainly because we hadn't shown the existing version to anyone. The new UI setup is aeons better than the old, although we're not done implementing it yet.