Miranda's only interesting as a love interest, particularly the renegade's romance.
The way the romance unfolds, with the renegade kiss starting it up, along with the "Love? I'm just trying to get you into bed" line. Before the suicide mission, when she tells you you need to come back to her, you say "no promises." She then fights along side you, quitting Cerberus after the fight.
Then you find her again in ME3, and reaffirm the romance. She tells you why she can't come with you, because she needs to find out how to save her sister. You ask to help, and she declines. If you say "be safe," she replies "No promises."
You help her out little by little from there as she hunts her father, now working with Cerberus, down. In the process she saves her sister, and gains valuable information for your cause. You arrive just in time to see her get revenge and save her sister, only to have her die in your arms.
See, that's damn fine characterization right there. Without the romance, not so much.