Recent reviews by Ernesti

Yes, buy and the game

+ loads of mods
+ good game modes
+ active developers
+ learn about spaceflight
+ fun to play
+ rewarding to achieve your own goals

drawbacks:
- lack of official multiplayer (KSP-Developer Squad uses the Unity Engine, and Unity is bad at networking)
- lack of Mod Management: for a Game that relies so heavily on Mods, the manual updating and unpacking etc. is quite the hassle. The Mod "KSP Mod Admin" for example does quite a good job at management, but that should really be part of the game.

all in all: I strongly recommend this game!