I think what I like about this episode is the theme which runs through so much of the Buffy series - the desire to be accepted, to be cool, to be popular. We've seen Buffy wrestle with her own secret desire to be normal, to not be the Slayer. Here we see Xander's inner yearnings for acceptance, to be part of the pack. What I like most is the parody of the cool group. Their pack behaviour becomes a caricature when they turn into a pack of hyenas - preying on the weak for their own amusement, and eventually, survival.
You can't help but think that Joss must have had some pretty horrible high school experiences, the way he really goes to town with the portrayal of the cool kids - showing them to be stupid, pack-like, unable to think on their own and looking like mindless idiots with the hysterical laughter after picking on someone they see as below them on the pecking order.
But there is a very dark message, as always, that comes with this fun - how easy it is to become that which you hate. That you should be careful what you wish for and that very easily the prey can become the hunter (and the hunter, the prey).
What I also like in this episode is that it gives Buffy and Willow a chance to develop their own friendship, without the input of Xander. It's the beginning of their steadfast friendship, and importantly we begin to see that whilst this is a friendship of three, it's also based on the foundations of strong friendships between the members of the trio.