The Genie Engine is a game engine developed by Ensemble Studios and used in several popular computer games, such as Age of Empires, Age of Empires II and its expansion (but is not used in other Ensemble Studios games) and Star Wars: Galactic Battlegrounds.
That's why SWGB feels like AoE2 in space. It uses the exact same game engine, modded into a Star Wars game. You take the very best RTS engine available at the time and make a Star Wars game with it? How can it possibly go wrong?
Star Wars Galactic Battlegrounds inherits a ton of features that made Age of Empires 2 and its expansions instant hits. The wide range of units available, how they interact in battle, the many ways to win (or lose), the obvious differences between factions and their unique units. These, among other things, made these games so precious. Oh and don't forget the farm queue!