Unlike on any other season before, Buffy and her friends are not the only collective fighting demons. This time, on season four, there is a whole other party involved, and a huge one. And in spite of that, the season hasn't been very loyal to that central storyline. Up to some point, at least. It's like the material to work with was so big it was hard to put it all together and make it work. But they did make it work eventually. Things really got going. It may be hard to believe how much some of the last episodes have to offer and how strong they are. Like this one.
Is it possible to have a dark secret kept long enough to be revealed in exactly the same episode where the heroes have to deal with it for good? "Primeval" is proof it is. Not to mention how the friendships and relationships in their midst have just been shaken and tested, at a time like this, when they need each other most. And even though this is, again, a TV show, not a huge budget production, there is something to look at in awe. This isn't just story-wise, it is visually impressive.
Friends realizing they may have been mad at each other for no good reason at all, the humanity in a human being painfully fighting computerized programming, old magic facing new technology, science going too far, one big interesting story coming to a powerful end.