Just as a counter-point for those still thinking about it, I'm someone that LOOOOVES minecraft, but hasn't been able to get into Terraria after a couple sessions. I'm probably going to give it one more shot, and if it doesn't grab me, that will be it.
I like the art (tall trees!) and the music. I like that there is a purpose for building (NPCs moving in). And I like that crafting is more rich from a practical
and just-for-looks angle than Minecraft is.
In fact, I like most of Terraria's broad strokes. But it's undone in the details.
The very small block size bothers me. The small blocks means it takes a long time to dig around, underground. Also important is the size of the blocks
relative to the player. It's annoying seeing spots I think I'll be able to fit through, only to continually realize I need to shave off another block to make it.
The control scheme is unwieldy. I quit yesterday after my Nth death played out the same way: mining underground, the light was beginning to get dim. So switch to my torches. Oops, now I'm being attacked. Switch to my sword. Oops, I didn't get a torch placed first, so now it's dark. And I'm dead. The player constantly has to switch between tool, light, and weapon. YES this is like Minecraft, but it feels much more frustrating, in Terraria.
Finally, the game's emphasis on extreme crafting I *thought* I would like. The ability to craft 100s or items like Chandeliers, chairs, tables, etc., I thought I would like. But in a weird way, all this choice takes away creativity, rather than supplies it. In Minecraft things must be fashioned out of blocks. But in Terraria they can just be auto-crafted.
Plus, there are way too many crafting stations. Every time I mined new stuff I would have to visit them all to see what new things I could make.
TL
R: Terraria is nice on paper but fails in its execution. Controls are clunky, and the very small block size makes the controls feel even clunkier.
Edit: Oh yeah, I totally forgot - I initially thought keeping your items upon death (and between worlds) was a huge
plus for Terraria, but it isn't. It's another example of gamers not always knowing what they want (and shows that Notch has great game design instincts). It removes all tension. Minecraft is fucking SCARY. Terraria isn't - it's low-stakes.