KSP is excellent. Sure, there's no time lag or relativistic effects, but it is hard, insofar as you have to understand staging (tsiolkovsky!), thrust vectoring,

KSP is excellent. Sure, there's no time lag or relativistic effects, but it is hard, insofar as you have to understand staging (tsiolkovsky!), thrust vectoring, and orbital mechanics. So, so satisfying executing a perfect Hohmann transfer, off the cuff, as precipitation is for suckers. If you enjoy the idea of space travel even slightly, and like the idea of having a semi-earnest crack at it - I can't recommend KSP enough. You get the full joy and frustration of sending a multi-probe mothership to Jupiter, using angular momentum to fling your subassemblies off, only to find that you fitted your landing struts upside down, and having to improv a "landing" using the fuel you'd planned to get home with to touch down. Then explode.