Mission: Space is the one EPCOT pavilion that is better now than it was when it opened. Having two distinct missions and the restaurant makes it feel more like a complete experience that's worth visiting more than once. I also appreciate that it is the spiritual successor to all the Disney trips to space that came before it (Flight to the Moon, Mission to Mars etc).
Having said that, it's still a weaker pavilion than it could be. Ideally, the "ride" would be like the Sea Cabs or Hydrolators, leading to a more extensive opportunity to learn about the red planet where we feel like we're actually there. As is, there isn't much to see in the queue and when you get off it's equally unimpressive. Its always been a "...that's, it?" kind of moment.
And as far as simulator rides, it's neither as fun as Star Tours nor as visually compelling as Soarin'. It has one major gimmick, and starts the ride with it, leaving the rest to feel a bit underwhelming. Again, the idea is stronger than the execution.
It's also unfortunate to have it in the same park with Soarin'. Green feels somewhat repetitive and less interesting because while the view is different, you don't get the variety of scenery that Soarin' has, nor the time to soak it in.