This certainly was the best 20 Euros ever spent on a game. I love this game, its learning curve and its modability.
Here a few pointers to help you decide:
1. If you love astronomy and space exploration, this game is for you!
You can do everything you have read and fantasized about. Build any rocket, no matter how stupid the concept may look at first and then try it out in the cold hard reality of space.
2. The game has a very steep learning curve and will constantly challenge you.
You will learn a lot about orbital mechanics, why staging is absolutely necessary and how to conserve fuel. If you don't, you probably won't make it into orbit, much less to the Mun or even other planets. Even after almost 600 hours of playing Kerbal Space Program, I'm learning stuff the hard way by losing vehicles and Kerbals.
3. The game developers actively encourage modding and the modding community is breathtakingly awesome.
The modability of this game is the hidden strength of this game. Without it, I wouldn't have played it half the time I actually did and wouldn't have enjoyed it as much at the same time.
The first time you play through the career mode (meaning you unlock all the technologies) you should play it without any mods, just to learn the basics, look how the game behaves, etc., but after that you should really check out http://kerbalspaceport.com/
(official mod download site) or the Kerbal Space Program forums. There's mods for so many aspects of the game...
Want to play in more realistic solar system where it's harder to even get into orbit? Check.
Want to have more realistic (= punishing) aerodynamics? Check.
Want to have rocket parts for even larger rockets? Check.
Want to have some autopilot capabilities to assist you with reptitive tasks? Check.
Want to have a warp drive? Also check.
There's so many more which you should probably explore for yourself. The replayability of this game is great, thanks to all those mods. The community forums are also really great and helpful.
If you play this game, please make sure you don't forget to mod it at some point, really!
You should not play this game,
- if you don't like space sims to be too realistic. Again: You will have to learn at least basic orbital mechanics which means the strongest force around is not your ship's drive, but gravity. And a heartless ♥♥♥♥♥ she is indeed...
- if you don't enjoy learning stuff the hard way by explosions, disintegrations and death. There is no perfect rocket. At some point stuff will blow up and you will have to start a whole mission again.
- if you don't like games that are still in development. There will be new versions released every now and then, so things change from time to time. For example, when the game was upgraded from 0.22 to 0.23, the whole science system got a rework and a lot of my rockets that were built specifically for science grinding became useless. The update was great though, since it got rid of grinding altogether.
I hope you enjoy this game as much as I still do. :)