They intrigue me for a different reason:

- The Fallen are space pirates either cast out from a greater civilization, or refugees from one that splintered through civil war or was shattered by some other means, perhaps even by the Darkness itself.

- The Hive also seem to be what's left of a race. In this case they used (dark? as in Darkness?) power to preserve themselves but it doesn't sound like there will be any more of them in our solar system than those who came or who are born / grown / whatevered here.

- The Vex too have this subtle air of desperation about them. They may be able to transverse time and distance, but their descriptions have them as worn and not at all new or off the assembly line. I get the sense that they, like the others, are here because either the Traveler, or the remnants of Humanity's Golden Age are essential to their survival.

But the Cabal. They seem to be an empire that is not broken. Instead they seem bent on domination and seem to have the means and manpower to achieve it. It feels to me that they are in our system not because they have to be like the other races, but because they want to be. If my speculation is even close then the Cabal are an intriguing and dangerous twist on the state of the other three races!