It's a simple concept but it's got a complex narrative. I think the director did a *REALLY* good job in helping the audience visually seperate out the timelines (plus, extreme kudos for the matching one into another).
Plus, starting with the dead ship with Mal falling into frame - seaming dead - with the soundtrack, is just a great way to start an episode. It grabs your attention, and just makes you go 'Hang on - huh?', but then also answers that question.
I often think show runners should be nailed to a chair and have people tell them why an episode worked, to be honest. Not the good ones, as the good ones understand. But if somebody had sat down with the people at Charmed and said LOOK, THIS IS A FUCKING GOOD EPISODE AND THIS IS WHY, they might have actually produced a decent run of episodes. Sadly, I don't think anybody did.