Buffy wanted to die. The whole 5th season led up to it, and to tell you the truth, it's pretty
morbid. Death was Buffy's
gift, according to the first slayer, and that's why I'm pissed off that she came back to life.
In one episode, Spike taught Buffy the reason that Slayers die. They want to die. Look at all the shit that Buffy went through. She was always the strong one, and she was always there for everyone, but she was always the one being hurt. It's amazing that it took her that long to die. There's a reason why Slayers never seem to survive for more than a year at best.
And also, I just want to point out a small plot problem - the prophecy talks about the blood of the Key, and yet, somehow, it takes Glory more than half a season to understand that the Key is a human? Oh well. I still liked the finale anyway, and I just wish that the show stopped there.
After seeing the resurrection, I am not nearly so pissed off. Buffy did go to heaven. Death was her gift. Her friends, ignorantly, wrenched her back from her perfect afterlife. It all makes sense.