Like any construction-centric game: Putting the finishing touches on a particularly large and complex ship, and then taking it out for a test-drive.
The destruction physics are a joy to behold. Crash two Large Ships into each-other, and watch their hulls warp and deform as they slowly crunch together into a barely-recognizable mess.
In multiplayer, fights between the nimble Small Ships involve lots of Old-School Dogfighting - requiring skill in the pilot's seat as well as effective design in your own fighter. That moment when you realize you've just destroyed your opponent's cockpit, main engines or power generator; disabling their ship and leaving them dead in the void; is a moment of victory.