If ever a measure of excitement prior to a game's release was needed, one simply has to look at the number of Let's Play videos littering YouTube based upon the beta versions of the game in question. Working on this theory, Kerbal Space Program is already a candidate for many people's Game of the Year.
Players take on the role of designing and piloting spacecraft capable of propelling their plucky astronauts, from the face of the planet Kerbin, and bringing glory to all Kerbal-kind. The appeal is clear to see; everybody loves a good sandbox game, so why limit yourself to a single world, when you could have a whole solar system (and potentially even more) at your fingertips?
Opening the Vehicle Assembly Building, you find yourself greeted by a legion of industrious Kerbals ready to construct your spacecraft. Vehicle assembly itself is relatively straightforward, with a vast array of components that snap together to create a near limitless variety of zany and implausible designs. Whether the resultant mass of metal and rocket fuel is capable of successfully leaving the atmosphere is another matter entirely.
Rockets can come in all shapes and sizes, with the ability to construct multi-stage vehicles, capable of jettisoning expended fuel tanks. In addition, there is scope for rovers, space planes, and some clever players have already constructed space stations and refueling platforms.
The lack of the planned campaign mode in the current release means there is little keeping you from building excessively over-engineered contraptions, as opposed to opting for the more cost effect approach that a limited budget would require. Details of the campaign are sketchy at best at the moment; one would imagine having to conduct a series of simple satellite launches before spending the big bucks attempting to land on the nearby Mün.
Community involvement looks set to be central to KSP's success; as well as the game's current expansive presence on YouTube, the SpacePort feature allows players to share custom ship parts and whole craft designs, along with distributing mods. There is one major downside to all of this however; the realisation that everyone else is significantly better than you at designing spacecraft.
As daunting as rudimentary astrophysics may seem at first, the game remains accessible without overwhelming; especially after working through the tutorial. After all, it's not exactly rocket science!