I really love the  game but it would be nice if they'd include some things to make the game a lot  more realistic. For instance, In Orion II, none of the worlds, not  even gas giants had moons. Also, all of the gas giants were all the same size and not one of them had rings. Having features such as this would make the game so  much more realistic.

We've been doing a ton of digging into current astronomical research, and I'm happy to report that many of the items you're asking for are in the design already. I've got a huge spreadsheet that I'm putting together with Tom Hughes, who's designing the Galaxy Builder, among other parts of the game. In particular:

 All planets can have moons, including gas giants. 
 Gas giants can certainly have Earth-sized moons. In rare cases, you can even get a double planet; we've seen double Jupiters in our simulations once in a while. 
 Asteroid belts are included, and they affect combat. Not sure exactly how stray asteroids will enter into the picture, but they'll certainly be considered. 
 We do have brown dwarfs -- that's basically the biggest-sized planet. Naturally, it takes a little time to get enough technology to make use of such things, but that's part of the fun of the game. 
 We don't have double stars; while such animals exist, our theory is that they're far less likely to contain habitable planets in stable orbits. And we already have lots of variety in the star types. If we want to implement multiple-star systems, we can simulate that quite effectively by simply placing two star systems really close together in the Galactic Map. 

Bottom line, in our philosophy, is that the gameplay has to come first. So any decisions we make based on "reality" also have to be fun. On the other hand, though, we're trying to be as realistic as we can. Tom and I are starting from true or projected facts and working outward. I think you'll like the system we've put together.