The love child of Minecraft and Metroid.
The best way to describe Terraria would be a cross between Metroidvania and Minecraft. Terrania is a 2D sandbox / sidescrolling free roam platformer / RPG that has its gameplay rooted in harvesting materials, building with those materials, exploration, and character progression. Combine these elements with the fact the worlds are randomly generated, staggeringly massive on the higher settings, and add in a multiplayer element, and you have a pretty interesting package oozing with potential.
Just by looking at the graphics or even the games mere 16 MB download size, it would be very easy for someone to completely dismiss the game at a glance. Make no mistake that inside is a very highly addictive game experience with a fair amount of depth and intricacies that make the game completely immersive despite its dismissive appearance.
The game starts with you creating a character from some basic options for your appearance, and then having the game randomly generate a world from 3 different size options, both of which are saved separately allowing you to take your character to other worlds and have other players come into yours via multiplayer. When the game starts you will find yourself outside somewhere with absolutely nothing except for a logging axe and a mining pick. It is from this humble beginning that your journey starts to explore your world, develop your character, and try to make a life for yourself.
The very first order of business is building yourself a base of operations on a place of your choosing. Chopping down trees for wood allows you to build a workbench, from that workbench are then able to build yourself some basic items like a wooden sword, walls, doors, and furniture. Crafting is key in Terraria, and the gathering of resources plays a huge role. Once you build your first dwelling, you will have a base of operations and NPC's will be available to move into your home. As you complete certain criteria in the game and build extra rooms and houses, useful NPC's will arrive in your settlement to provide you with goods and services. As an example, if you get more than 50 silver and have an extra house space, you will attract a merchant. If you find extra heart containers (the only way to raise your max HP since there are no levels or exp) you will attract a nurse who can heal you for a small fee.
In between building your home base, you will spend the bulk of your time exploring the world you find yourself in, scouring the depths for resources and special items. On the "large" world setting, the map is staggering massive to the point where I can't even begin to explain it. Roughly 80% of the maps you explore are underground and involved lots of digging around to navigate. The caverns are dark and monsters roam around trying to kill you. So the questions begs what exactly are you looking for down there?
It does warrant mentioning that given this is a true sandbox in every sense of the word, there is no winning the game or a defining moment where you declare victory with fanfare. The game is what ever you decide to make of it, although since the deeper you go the harder things get, advancement of your character in terms of weapons, armor, and utility items will probably be goal enough for many. Heart containers to raise your max life are hidden deep in the many layers of the underworld. Treasure boxes while very rare contains some key items you would expect to find in any Metroid or Castlevania to make your life and exploring in general a lot easier. Flippers that allow you to swim in water, an item allowing underwater breathing, advanced light sources, grappling items, and jumping boosts just to name a few. In addition to these, you will find better and rarer materials used in the games crafting system to build stronger armor, a variety of difference weapons, and other utility type items.
During all your exploring and building, the game sometimes likes to throw curve balls at you to spice things up. The game has a natural day and night cycle in which night produces a variety of undead and stronger monsters akin to Castlevania 2. Occasionally a blood moon could lead to your compound getting assaulted by undead, or a goblin invasion might try to make life on the surface difficult. The game does contain 3 bosses currently, some of which are summoned, some can show up to cause havoc for you. Defeating a specific boss opens up access to a high end dungeon area somewhere in your world which is supposed to contain some of tougher enemies in the game as well as some of the better loot. Factor in multiplayer where you can team up with friends and explore and tackle bosses together and you have a pretty interesting package.
Terraria's developers have made no qualms about calling the game unfinished and still a work in progress. Despite that, this is one of the funnest and addictive unfinished games I have played, and I've played my fair share. The framework in place is sure to make hours seems like minutes and chances are if this is the sort of game you like, you will be sure to get your $10 worth especially with high replayability with multiple character and world slots and randomly generated terrain. If you are looking for a more defined experience with a clear cut end boss or objectives, or don't like spending time designing and building which dominates a lot of the early few hours of the game, then I'd recommend a pass on this. A lot more content and support is promised, so hopefully it will be just as fun watching the game grow as it is to play it.