The speaker is so interesting because of what she sets out to do in the course of the poem.  There is an obvious connection with the father that is complex and intricate.  On one hand, there was a feeling of love and awe that the child held towards the father.  Yet, there is a now dominant need to remove the presence of the father from the child's life, a presence that seems to have contributed to the child being the way she is today.  There seems to be some hope that in eliminating this influence, life for the child can be better.  The idea in "Daddy, I have had to kill you" is something that brings out the intensity of needing to rid herself of this influence.  What makes the speaker so interesting is this purging, this almost intense ceremony in which the speaker must eliminate and remove the father from her life.  She is incapable of feeling anything but this, incapable of experiencing anything other than how much she is driven by the need to remove him.  It is this element that becomes interesting in the speaker's consciousness in tracing how much this relationship has fragmented.  From a point where the speaker was either in love with or in simply worship to a point where there has to be this shedding is a transformative relationship that seeks to remove an influence.  The interesting notion out of this is whether or not the speaker really has removed the influence of the father, or whether by continually seeking to remove him from her life she has actually resurrected his spectre back into her being.  To probe the depths of this is interesting, its implications profound.