Good concept, poor execution.
Start with Terraria, then add a plot-line, high-res graphics, and cool concepts like airships and sky whales, etc. From there, take away usable controls, tolerable interfaces, decent animation, functional map areas, etc.
Getting around the place is a pain because inertia is handled poorly, so you feel like you're on skates sometimes, and jumping feels very awkward.
The interfaces are similar to what you'd find in other games of the genere, and they're nicely drawn, but they're ergonomically frustrating. You figure them out after playing with them for a while, but they seem to have only the bare minimum of functionality required to use them. Why can't I use the mouse wheel to change between items in my hotbar? When I craft a workstation, why do I have to place it in my hotbar and then select it and use it in order to place it?
The character animations look pretty damned stupid, (this is common for games that try to use hand-drawn art, but in this case it's exaggerated because the guy re-orients his limbs and torso to look at the cursor and ends up looking like a marionette).
The maps are sort of ridiculous. Yeah, you're way up in the air in a world that apparently has poisonous gas instead of a surface. The game autosaves from time to time, so if you manage to fall, you'd better just break out and load the last autosave immediately. If you let it go for a screen or two it's going to save while you're falling, and your descent is going to pass several screens and end with your doom. You don't respawn either. If you die it's game over, and you can load a save. It does keep 2 autosaves, but it seems like a far better solution to just design sane areas.
Hit boxes are almost like an experience in coin flipping, which is exacerbated by the fact that your weapon fire is not precise, so even if you manage to aim perfectly at the high speed critters that are whipping back and forth again and again like ducks in a shooting gallery, you have to fire three or four times to get a straight shot, and then the bullet has a 50/50 chance of passing right through the thing.
You think I'm exaggerating? Try mining something. You stand right next to a stationary object with the jackhammer out and you place the cursor over the tile you want to mine. Something else gets torn up, probably in the background somewhere, and you have to creep the mouse around in circles until you find whatever bizarre sweet-spot the tile's hit-box is on. Want to mine the tile immediately beneath that one? Well, you can try moving the cursor straight downward, but honestly it's a crap shoot. You may or may not end up mining the tile you're after.
In any case, considering that Terraria sells for $10 at full price and $2 on sale, I'm sort of miffed that I kept this $15 turd on my wishlist for so long. I was excited when I finally got my hands on it, and pretty badly disappointed when I finally played it.