I always thought that Navy ranks would be much more appropriate for Space 4X games. Horatio Hornblower far from his superiors, having to make decisions on his own, etc...
But, to be fair, when/if we ever start sending ships into deep space with humans on them, it'll probably be the Air Force that does it...and they use a modified Army naming system for ranks.
But "Admiral" still sounds better to me than "General"