I think every death was essential to the story.
Do I LIKE every death that happened? No.
Jenny's death, as the first meaningful death of the Buffyverse, is definitely one that needed to happen. Well, in that way I mean, someone had to die for the audience to realize that Angelus really is a monster. I'm surprised Willow wasn't killed in the hallway in "Innocence", though it would have sucked. One reason I love "The Vampire Diaries" is Kevin Williamson isn't afraid to kill off major players. Despite fan attraction to a character.
Joyce's death was amazing because it showed there are some things Buffy just can't fight. And it showed how unexpected death can be. And we got the most amazing hour of television out of it. Seriously, if you don't like "the Body" something is wrong with you.
Tara's death kills me when I see it because it was so.. meaningless. In the terms of the show, it brought out Dark Willow and progressed the addicted Willow storyline, but death by stray bullet is just.. almost an insult. Not that I'm saying that Joss or Marti is insulting Tara, but that death like that, being an innocent bystander and getting the fatal bullet is so gut-wrenching.
You can't be mad at Anya's death. I'm sorry. Emma wanted Anya to die in the battle because she didnt want to do anything after the finale. As well, giving up her life is the ending to the story. She started out as this demon-turned-human, and by the end she is a human who used to be a demon. Get it?
Cordy's death sucks as well. The whole Cordy storyline of s4-5 was awful, and it makes me mad that Joss ruined the character in s4 to essentially get back at Charisma for getting pregnant and keeping it under wraps for so long at the beginning of the season because it screwed with his vision of the season. I'm sorry, life happens Joss! But I do realize had Cordy been awake when "Home" happened, they most likely would NOT have left the Hyperion, thus prohibiting the season 5 we know from happening. Maybe she could have woken up and not died though? Help Angel get back to where he belongs? Though, I know that when they were shooting "You're Welcome," Joss still thought they'd get picked up for a sixth and final season, so he probably was gonna use her in s6 some as well.
Fred's death is one of my favorites to watch. She was definitely my favorite main character in Angel. And I cry every time I see "A Hole In The World". I hated it when I first saw it, but it showed how magnificent Fred as a character is, and how much she means to each of the men in her life. One thing that sucked is Wes and Fred JUST hooked up the episode before. Illyria is a good character, and I wish we could have seen more of the Fred continue to come out in season 6. (I refuse to read After The Fall after the fifth issue because I hated the direction it was taking, and I know it would have been different if the WB wouldn't have cancelled "Angel" because Joss wrote the series finale like it was because he KNEW it was the last episode. It would have been tweaked if it was just a season finale, and I'm 80% sure Wesley wouldn't have died.