Not a "minecraft" clone.
The crafting is quite simple all you need to do is stand by a workstation and if you have the required components the recipe will show up.
As for the world size it really isn't that big, at least not horizontally. However the world is quite deep. You have three different levels underground: dirt layer, rock layer and hell. Depending on the size of the map the layers grow deeper. For example at small size you reach hell at around 1500 feet. At medium you encounter hell at 2300 feet. Beware however if you aren't geared for hell you will die quite quickly to the fire imps. Unlike most other monsters in Terraria(except bosses) fire imps can hit you through walls with their fireballs. They also teleport around.
There is also a dungeon, with a boss that must be killed during night, to enter. There are floating island with treasure. There is an underground jungle.
As for a "clone" Terraria has very little to do with Minecraft. Minecraft is more about exploring your creativity and not that much about the actual adventure. Now Terraria is however very much like the game "Digger(AmigaCD32, 1993)". The only difference between the two games is that in Diggers you were fighting an enemy faction to the death. The concept was identical. You could say that Minecraft/Terraria is a clean rip-off of Diggers. Now many of you have probably never played Diggers and you really missed out on something that was so unique and ahead of it's time.
But there is no point comparing games at the end of the day. Terraria stands on it's own due to its immense fun factor once you get the hang of it. While Terraria has a slightly better "start" than Minecraf(which has none), they both really need help on that part.
Another thing that i hear a lot of complains about are the green slimes at the beginning of the game. I agree that the *green* slime spawn should be looked at during the first few "in-game" days.
Terraria is very addictive and you do *not* need to be "creative" to enjoy it(unlike Minecraft).
I might add that the multiplayer is complicated just as minecraft. You need someones ip-address to be able to play on their server. There is no in-game server browser and many servers have quite annoying lag problems where monsters "warp" around. What is needed from the Terraria developers to do 1) Create a stand-alone server. 2) In-game server browser. 3) Cheat protection. There are more things but those are the most urgent ones.