"Isn't this just Minecraft?" Let me explain the finer points.
I figured we'd get a lot of thoughtless threads in here immediately going HEY, THIS IS RIPPING OFF MINECRAFT so I thought I would help to compare the two games for people who have either never played either game, or have played Minecraft and are on the fence about Terraria, and a lot of people coming in and saying "pfft, Minecraft is so much better!" without elaborating probably isn't helping anyone make a decision on the matter.
But first, let me make one thing clear that a lot of people forget:
It's okay to like two games even though they're similar.
A lot of people seem to think that you can only like one or the other. There's no logical reason to think that way. I like both games for different reasons. This same problem just recently cropped up on the Dwarfs?! forum too. I don't understand why a person can't like two similar games, but oh well.
Let me explain the focuses of both games.
MINECRAFT: The focus is on building, either building through placement or "subtractive" building, like in caves and such. If you prefer something slower paced, Minecraft may be what you want to stick with. It has a zillion different types of blocks to build with and you can wire contraptions together, so if you want to do more building and relaxing, Minecraft is always the best choice.
TERRARIA: The focus is on adventuring. Though you can and are encouraged to build, it is not the focus and there's rarely enough downtime to relax and build as even during the day, monsters are about. Terraria's adventuring aspect is much improved over Minecraft's. There are many different types of monsters, the combat is much more fast-paced, there are bosses to conquer, dungeons to explore, and the underground has much more gameplay opportunity (jars to break, many more treasure chests to find than in Minecraft, unique weapons, etc.)
Both games are unimpressive from a technical graphics standpoint. Neither game is for someone looking to test out their latest rig, so that's just something to keep in mind. If you want immersion, Minecraft is played from a first person perspective and may offer you more. If you prefer visibility, Terraria is very pleasing.
Both games offer a similar crafting experience. There are many, many objects to craft.
Terraria offers things in this respect Minecraft does not, such as tables, chairs, chandeliers, potted plants, and things like that. Some major things Minecraft has that Terraria does not would be things like wired contraptions and transportation via mine carts.
Terraria does have its own fun form of travel though, in that you can create a hookshot-like device to pull yourself around and hang from walls/ceilings. It's really cool.
Terraria has a really cool Castlevania type of feel. I don't know if it's just me, or if that jives with anyone else. This may be a factor for some people if they get a shot of nostalgia out of playing it.
Terraria has a magic system, though it's not as fleshed out quite yet as I would like it to be. If you like the prospect of magic, Terraria is a good choice. If you don't like magic, Minecraft is devoid of it, and may be a better choice for you.
Terraria currently has no farming or food processing. Minecraft does. You can, however, plant trees in Terraria. If you were looking forward to doing farming though, Terraria won't quite have your needs covered.
BOTH games seem to be in an unfinished state. Terraria is much more functional and complete, but with the promise of more coming due to a few lacking features. Multiplayer games can be enjoyed without things that constantly plague Minecraft games, like chunk errors and glitches with players being invisible. Also, everything that is in Terraria actually works. There are a few things in Minecraft that are very buggy or simply don't work.
The price of each respective game is, in my opinion, fair game for discussion. Minecraft, despite its many issues and beta status, costs over $20 (a lot of money to drop on a beta experience!). When the final version is released, it will cost $28.
Terraria costs only $10, and is far more functional despite having a shorter development cycle. If you're looking for stability and cost friendliness, you may want to consider Terraria.
Currently there is no basis for comparison as far as update frequency. Updates do take a little longer than desired in Minecraft (very few meaningful updates spread over long periods of time), but we're not sure if Terraria will take longer or shorter to receive similar meaningful updates.
Avatars in Minecraft can be changed to any texture you like. This offers a bit more freedom than Terraria, where you have a selection of hair styles, and then skin/hair/clothing colors. While Minecraft does offer more freedom in this regard, I do still think it's commendable that you can make orcs, trolls, dwarfs, and things like that in Terraria if you're creative with the limitations, but ultimately Minecraft allows more freedom.
Which game do I personally like better?
I like Terraria better at the moment, however my opinion may be tainted by the fact that I've played Minecraft to the point where everything has become routine and I am no longer as impressed with it. Ideally, you should try both games if you own neither, and decide which is best for you.
If you're still having a blast with Minecraft, you may want to hold off on Terraria. If Minecraft is becoming routine for you like it was for me and my friend, Terraria gave us a big shot in the arm of adrenaline. We're laughing and getting slaughtered and having a grand old time.
Hopefully I've cleared up any finer points for people who were interested!
