I bought Kerbal Space Program back in 2011, when it offered only a small fraction of the features available now. Even then it was worth it, and it's only gotten better since. I've had more fun and wonder and learned more about rocket science (really) than I ever would have anticipated. The game is fantastic, and I can't recommend it highly enough.
I have never encountered a game that enthralled me as this one did. After being introduced by a friend - he challenged me for a race to the moon, which, surprisingly, I won - I played this game feverishly every day, some nights.
Prepare for sleepless nights and cancel every plan you may have for your life - it will consist entirely of Kerbal Space Program. This game will become your dinner date, your bed partner, your counselor. It is that good.
I spent hours, including watching youtube videos how to place the engines in the advanced construction and it never works. It is extremely frustrating and deffinitely not enjoyable experience.
I've been with this game since the beginning. Loved every single stage of the development. Developers seem to listen to the community. The mods are amazing, and I like the close knit aspect of sharing pictures of amazing landscapes and best space stations, swapping parts, etc. I make something new every single time I play. I now have a 3 year old daughter and she hasn't hit orbit quite yet but she's getting the hang of more boosters dadda. Short answer, best game ever. Only limit is the time you can dedicate while giggling uncontrollably as my new contraption sends brave Jeb flying when he shouldn't have. The best part about this is that I can bond with my kid over my love of the stars. I might not know much but I couldn't be prouder when she pulled out her 2x little plastic telescope, aimed it at the moon and said, "Look Dad, we landed there." One request - developer supported multiplayer, maybe as a DLC or something. I'd be happy to pay for the time you put it and can't imagine the various difficulties that come with linking up the different times/parts etc. Thank you! See you at 2K hours haha!