Why i like about Orbiter :
-it is a simulation that does not try to hide behind arcade design, it is trying to offer as a realistic experience as possible of the physics and how space vessels are working, and is so brillantly setup that it is very accessible after reading some very well done tutorial.
-while playing you always learn something and you are then enticed to search for more info/knowledge about space, objects and the universe, because you always want to know more.
-its scope is beyond the majority of the other usual sims with a full scale solar system and with addons even more to never be able to see everything.
-it is the perfect sandbox/open ended/freeroaming software for me, i can do what i want, when i want and how i want without being limited by the same scenarios.
-half a billion of addons of any kind, realistic, scifi, fun, weird, etc... that will always fit any scenarios that can come to my mind : recreate a real space mission trying to stick to the plan, fly some insane alien aircraft over the star war death star, etc...
-it remains the closest thing to the old childhood dream of really going to space, explore the solar system, etc...