Terraria is all about the crafting that it forgets to focus on core gameplay by offering balancing issues and bad appeal
When you start up Terraria for the first time you are instructed to create your very first character to explore the vast expansive worlds of Terraria. Now, as well as a few similar and crazy hairstyles, there's not much at your disposal to customize your character. Besides hairstyles, there is nothing to change, merely altar the colour, and even that is a little bit frustrating, as you use those RGB sliders. Most people, unless you want to be really picky because for the majority of the time you will wear armour anyway, will just keep the character as the default look. There is nothing wrong with this though, in-fact if you move the sliders to attempt to change the character you normally end up completely ruining it anyway. On the other hand, customization of armour and weapons when you get into the game is much, and I mean much better. Think of a random weapon or armour style in your head, and it is probably craft-able in Terraria. Ranging from the simple crafted items early on such as copper swords and basic handguns found in some underground caves, to star cannons, massive lava flails and even lightsabers! Armour varies a lot too, and if you want survive after nightfall when the zombies and weird floating eyeballs are out to kill you, your going to need to know which armour as better for your style of play. Want to rummage through underground caves without the need for torches? Go for the molten armour, which is also the most defensive armour. Use a lot of mana? Meteor armour is best for you. Or how about for moving round really quickly? How about shadow armour? The possibilities are endless! However, if your new to the games were you have to craft items, your not going to like crafting all your stuff. Even people who have experience with this style of games, or have played minecraft etc... May be a little confused on how to start crafting as its rather confusing.
This brings me to my next point, Terraria doesn't seem to want to teach people how to play there game at all. There's no tutorial mode, only a guide there which gives you very vague hints and tips now and again on how to do things, sometimes this doesn't really help at all either. The only way your going to even learn much about Terraria is if you have numerous hours on your hands to read through an entire wiki site dedicated to Terraria. That's what I did anyway. Or if you have a few friends that will teach you after they've read the entire wiki.
The game-play mainly consists of crafting better and better items to survive in your randomly generated world and fend off enemies during the night. However if you build a house to stay in at night, you probably wont have much problems with enemies during the night. Also, Terraria does a good job of adding a different variety of random events to the game to vary it up a little at night. At times a bloodshot moon will occur and enemies will spawn at twice the rate and be twice as hard to defeat and be twice as powerful. Sometimes a massive goblin army will start to march towards your house and try to defeat you. And by defeating these this can normally get you some very respectable rewards. However these events don't happen on a regular enough basis, and so you can get bored of continuously fending off zombies as you try to build your house during the night. And your first shadow orb encounter can be a fun but surprising one. Unless you read the wiki, you'll try hitting it, it will disappear and an enemy boss, the eater of worlds will appear. Now if your unprepared, then be ready to die tonnes of times before you defeat him, because he will follow you whenever you spawn until you kill him, and he has tonnes of HP.
These random events and enemy boss fights can make multi-player and playing with friends a blast. And what's more, opening up multi-player gives you and your friends even more choices to make on were to go and what to do! As long as your friends aren't jerks, you should have no trouble with massive boss fights as long as your mate doesn't keep spawning them.
Recently Terraria released a new patch which contained a variety of new mobs such as jungles, bats and bigger deserts. The new mobs are great, but some rarely appear, and it's frustrating when you can't find the one your looking for. And as if deserts weren't annoying enough, we all know not to build on sand right? Well they've made the deserts bigger, and to add to the pain, cacti. These aren't just background textures, but actual cactus. These are very, painfully annoying. There is a trick to mine the sand underneath it and it will just disappear, but to the average gamer who doesn't read wiki's, you can't jump over them and they take ages to break down depending on your tool set.
Overall, Terraria is a good enough game to have you playing for a long time, and there is enough new content in there to keep you playing for a long amount of time, but some things may not appeal to the more casual gamers such as the crafting system which can be over-complicated, and the mobs need to be balanced out a lot.