Spectacular game! It's fun and tense!
Kerbal Space Program is an immersive experience! From your first orbit to your first moon landing, the emotions you get from this game are unreal. It's truly, outright epic.
The difficulty can vary, going into orbit is easy (although on the beginning is hard as hell) but traveling to the outskirts of the kerbol system is insanely hard.
Learning how to play can be hard, but it's very rewarding. The tension of the gameplay is phenomenal, you'll be clenching when trying to land or to get a maneuver right.
I would recommend this game to anyone, and what's great is that KSP is mod friendly so the possibilities of your experience are endless. Make sure you have a good PC, because this game is very demanding.
Seriously just buy this game!