I agree and disagree.
Agree because she was one of Voldemort's most trusted and reliable death eaters.
Disagree because there were "more" death eaters that were much better than her. Wormtail and Snape for example. I'm sure Voldemort had other "death eaters" he could equally trust with Bellatrix, like Snape.
I love how Helena Bonham Carter painted the image in my head of this super-mental woman, it was almost exactly how I imagined she would be! I think she's a great character, insane. I also think that she might have a mini-crush on Voldemort. ayehhh!!!