This is an innovative, engaging "sandbox" game that is one of the best value offerings out there.
For those looking to find out what the hype about "sandbox" games is all about, this is the best first stop. It is a fast-playing side-scroller along the lines of the platformers of old (Super Mario Brothers, etc.), but set in a huge world where you can explore, do battle with monsters, build up, and destroy as much as you please.
At first, gameplay may seem fairly straightforward - platforming, fighting monsters, gathering items. But the innovation comes in the ability to completely alter the face of the world - dig out caves and tunnels, mine ore, build shelters and fortifications, destroy obstacles, disarm traps, and literally shape the world to look the way you want it to look. To do that, however, you will need to explore to get the tools, ore, and other supplies you will need to reshape the world.
The beauty of the game system is in how the different sub-systems interlock. To build, you will need the right gear and raw materials; to get gear and raw materials, you will need to explore and fight monsters; to explore and fight monsters, you will need the right gear and a secure base of operations to work from; to get a secure base of operations, you will need to build it yourself; etc., etc. Each of the game's different themes naturally contribute to each other.
Graphics, Controls, Sound:
The graphics are necessarily limited based on the "retro" look styled after the platformers of old, but are colorful and attractive, and the (deliberate) pixeled style is not distracting. Controls are intuitive and responsive. Sound is charming but minimal.
One problem with the game is the naturally limitations imposed by the two-dimensional environment, which of course is by design, but still clunky to work in for those who are accustomed to three dimensions. Also, combat can be a bit simplistic, although again this is in keeping with the game's retro theme. Crafting recipes can be extremely unintuitive, although the Guide (an in-game NPC) is indispensable for figuring them out - but there will still be many trips to the (excellent) Terraria Wiki.
The biggest problem, however, is that support for the game is being discontinued. Too soon, in my view; this game still had further developments that could have enriched it. Here is to hoping that further sandbox-type games by the same or other developers are on the horizon.