The Rachel Dawes character was anyway pointless, but I thought Katie Holmes did the best she could and came off as a fairly likable character.
Gyllenhaal's version, on the other hand...ugh. I wouldn't care about her looks being average if she had a strong character or a memorable performance to compensate, but there's just nothing there. Her connection to Bruce is tenuous (she already put him in the friend zone without dating him once and has already secured a much more stable rebound, but Bruce still has the hots for her because...reasons), and she's not written with much of a personality, so the only thing left to focus on is that awful cracking voice that makes all of her "taking a stand" moments come off like a teenager arguing with her parents.
It's not the level of annoyance, it's that there's nothing to her but the annoyance.