Basically, this game is awesome.

Cool orbital mechanics, space that actually works like space, lots of things to do. Hard to explain WHY the game is so much fun. It just feels very good to plan a complex mission, have everything go wrong, and then solve the problems that occured in some creative way.

For example, today i launched a rocket that should transport a Kerbal in a rover to the Mun, then dock again in Orbit and bring him back to Kerbin as a test for my interplanatary program. So when i got to the Mun, i noticed that i a) built the decoupler incorrectly on the main vessel so its docking port couldn't be reached, and b) Forgot to attach engines to the Lunar rover. So i decided to just let him in Munar orbit indefinitively, and send a second similar vessel with these problems fixed. Only i didn't have enough fuel on board the rover to get into Munar orbit again. Then i had a genius revelation. I could use the main vessel with the working docking port to save Jeremiah from his Munar orbit, crash the bad rocket into the Mun, and build a third unmanned rocket to save Bill who was stuck in his rover on the Mun. Luckily i didn't have to land exactly on top of him since my rover had wheels. So Bill grabs all the Science from the rover and flies back to Kerbin, Jeremiah gets rescued by Bills vessel, and everyone is happy.

Also, it has probably the most accurate depiction of Space you have ever seen in a game, while still being easy to understand and play. Gravity works like it should, orbits move like they should, you can do cool stuff like gravity assists to save fuel, but all of this is not necessary to play the game, it just makes you feel good if you pull it off correctly.

Finally, regarding the early access thing: My policy is to only buy games when i think that what i get RIGHT NOW is worth the money. If you are in any way interested in space (and seriously, who isn't), KSP is already worth your money at this stage. Anything that gets added in the future is just a bonus on top of that.

Basically, this game is awesome. Cool orbital mechanics, space that actually works like space, lots of things to do. Hard to explain WHY the game is so much fun. It just feels very good to plan a complex mission, have everything go wrong, and then solve the problems that occured in some creative way. For example, today i launched a rocket that should transport a Kerbal in a rover to the Mun, then dock again in Orbit and bring him back to Kerbin as a test for my interplanatary program. So when i got to the Mun, i noticed that i a) built the decoupler incorrectly on the main vessel so its docking port couldn't be reached, and b) Forgot to attach engines to the Lunar rover. So i decided to just let him in Munar orbit indefinitively, and send a second similar vessel with these problems fixed. Only i didn't have enough fuel on board the rover to get into Munar orbit again. Then i had a genius revelation. I could use the main vessel with the working docking port to save Jeremiah from his Munar orbit, crash the bad rocket into the Mun, and build a third unmanned rocket to save Bill who was stuck in his rover on the Mun. Luckily i didn't have to land exactly on top of him since my rover had wheels. So Bill grabs all the Science from the rover and flies back to Kerbin, Jeremiah gets rescued by Bills vessel, and everyone is happy. Also, it has probably the most accurate depiction of Space you have ever seen in a game, while still being easy to understand and play. Gravity works like it should, orbits move like they should, you can do cool stuff like gravity assists to save fuel, but all of this is not necessary to play the game, it just makes you feel good if you pull it off correctly. Finally, regarding the early access thing: My policy is to only buy games when i think that what i get RIGHT NOW is worth the money. If you are in any way interested in space (and seriously, who isn't), KSP is already worth your money at this stage. Anything that gets added in the future is just a bonus on top of that.