Ugh, she pisses me off to no end! Easily, my least favorite character. She was so immature and selfish, whiny and annoying... I could definitely do without her in the entire series.
Although, one of my favorite episodes is The Gift, and Dawn was essential in that episode. BUT, without Dawn that episode could easily still have great significance. Buffy still could have sacrificed herself to save the world and it still would've been epic.