This episode introduces several key elements that will resurface later on in the Batman animated universe (as well as the rest of the DC Animated Universe), the most important being the introduction of Talia, a skilled and ruthless beautiful woman and potential love interest for Bruce Wayne/Batman (she does find out his true identity in this episode) who rarely can be trusted (as she demonstrates towards the end of the episode), and the Society of Shadows (or Assassins), lead by Ra's al Ghul, who only has a small cameo at the end of the episode, foreshadowing the events to come.
To be honest, the first time I watched this episode I was not familiar with or even heard about Ra's (Batman: TAS was one of the first super hero shows I watched that also got me into comics (DC Comics that is, as the 90's FOX X-Men animated series is the one responsible for my love of Marvel Comics), so I had no idea who he was or what he is able to do, but one thing was certain: he would appear again as Batman's enemy and he will be big trouble. His small appearance here creates a great cliffhanger and a turning point in Batman's career. As a bonus, David Warner does a great job at voicing Ra's (although briefly), and you can tell he's more dangerous than he looks.
The main villain used in this episode (probably mainly to conceal Ra's true leading position and to allow Batman and Talia to "work" together) is a character called Count Vertigo, who if I'm not mistaking is primarily a foe of Green Arrow in the comics. He seems interesting enough, able to provide an occasional threat to Batman, and it would have been nice to see him again after this episode's climax. Although clearly not set in the same continuity, he does appear as a villain in an episode of The Batman, where Batman teams up with Green Arrow to stop him, is worth mentioning.
Among other memorable or interesting things to note about this episode, Batman's first encounter with the Shadow warriors, the chemistry between Batman and Talia, Batman's "trick" to counter Vertigo's powers and the homage to Alfred Hitchcock's movie Vertigo come to mind.
Overall this is a good episode; even though many people consider it only a filler episode and it's real purpose was only to introduce us to Talia and Ra's, this episode gives us a coherent story and doesn't disappoint.