I guess I'd call it fairly deep, yet accessible. All the choice with the tech trees and upgrades is a bit overwhelming for a new player, but I just play and learn it bit by bit.

Currently there's TEC factions (each now has loyalist and rebel subfactions) and Advent factions. I don't yet know if they have major differences, but at least not visual ones.

I guess I'd recommend this rather than the expansions, since this has all of their features too. It's a long time since I played the last one but I think that the models now have more polygons and more detailed textures.

Overall though, it is and feels like SoaSE with add-ons, so if you've played the old one, the experience won't feel new.