Can anyone explain as to what this game provides over the well-developed Orbiter (http://orbit.medphys.ucl.ac.uk/) aside from the build-your-own-space-launch-system angle?
Orbiter is not really a game. Its UI is terrible, it’s full of complexity, all that. Now, that’s all fine for a simulator, but not for a game.
If you want a game that gives you better feedback and a much better UI and much more laser-focused prioritization of what’s actually important and essential to putting space travel in a game, then you want KSP.
Orbiter to KSP is like Garry’s Mod (only less accessible and even less of a game) to Minecraft.
Comparing the two doesn’t even make that much sense. You get vastly different things out of them.
(Also, it’s arguably more beautiful to look at.)
The chance to build, launch, and crash your very own space jalopy ought to be worth the price of admission on it's own, though!