KSP is going to be the best game ever. When you first start playing, its ridiculously fun. You're trying to get into space, and you have no idea what you're doing. Your first few launches you will either end up still on the launchpad, or in 10 pieces falling back to Kearth. When you finally manage to do get into orbit after 20 or so failed designs, it's an awesome feeling.
I started playing during 0.8 where all you could really do was orbit the planet, which was fun for awhile, but eventually I got bored of it. When they add space stations or other planets I'll never stop playing.