Like the original Star Wars arcade game, The Empire Strikes back was also a vector based game. In fact, it was released as a conversion kit for Star Wars. The Empire Strikes Back was actually the third Star Wars arcade game. Return of the Jedi came out before Empire though it was not a vector based game.
The Empire Strikes Back is more rare than Star Wars since Empire was only available as a conversion. Many operators did not want to "upgrade" their successful Star Wars game. Despite some graphical improvements with Empire, I think many people (myself included) preferred the original.
Game play is actually very similar. In Empire Strikes Back there are four distinct stages. In the first you are hunting for and destroying Imperial probe droids. In the second you are defending the Rebel shield generator form Imperial AT-ST and AT-AT walkers. In both of these you are piloting a snow speeder. In the third stage you take the role of Han Solo in the Millennium Falcon fighting your way through a swarm of Tie Fighters. In the fourth stage, still in the Falcon, your goal is simply to survive an asteroid field. The stages then repeat with increasing difficulty.