"Every one of your accomplishments is due to your skill. The only things I can take credit for, are my mistakes."
Unfortunately, Miranda's probably one of the most unfairly and widely reviled and bashed characters in the Mass Effect franchise, with most other members of the ME fandom being content to treat her like the Anti-Christ. Myself, I love her for the following, simple reasons: Beauty, Brains, Badassery, and a hidden heart of gold.
The Beauty part is obvious. Her sexiness and hotness are such that she actually gets flak for it (which makes no sense). Me though, I appreciate both her lovely low-cut catsuit and also her very pretty face that comes from her voice actor, the very attractive Yvonne Strahovski. I also like how they made her a brunette, since I do tend to have that preference.
As for brains and badassery, she was the head of the Lazarus Project that brought back Commander Shepard back from the dead and in so doing gave the trilogy's hero(ine) a second chance at life and the opportunity to stop the Reapers for good. Shepard owes their very life to her. She's also a woman of tastes and culture, liking classical music and clearly favoring the sophisticated over the, well...unsophisticated. Some use this to claim she's arrogant, but it's a rather ludicrous claim in view of the above quote plus the following lines:
"The difference between you and me is, you were great before we brought you back...I'm great because of it."
(In response to Shepard's noting that Miranda sounds like she was designed to be perfect): "Maybe, but I'm not. I'm still human, Shepard. I make mistakes like everyone else. And when I do, the consequences are severe."
So, in addition to being smart and sexy, she's also modest to a fault. Yet another good quality (if not also unfortunately taken too far due to her self-loathing, but this can be rectified by Shepard showing her care).
As for badassery, she lists her combat qualifications early on, and while a bit more fragile than some of Shepard's other crew-mates, she is still capable of holding her own in a fight, and in fact all of her special abilities are geared towards offense (including Overload for synthetic foes, and Biotic Warp for organics).
Lastly, we have that hidden heart of gold I mentioned earlier. Despite most members of the fandom's claims to the contrary, Miranda is not only not as arrogant or mean as she appears early in her debut game, but she is also not a monster simply for working for Cerberus. Instead, she's an example of a morally gray but well meaning person who happens to be aligned with the wrong people (who she ultimately abandons). Miranda is also very warm, polite, and pleasant when speaking to Shepard on the Normandy, and so long as she is shown civility in turn she continues to give it. She doesn't fail to praise Shepard's successes and accomplishments (even when she is colder to him/her, she admits that she has respect for their abilities), and she also has a genuine and earnest desire to see humanity succeed that is not twisted and perverted by xenophobia the way it is with most Cerberus members (and in fact Miranda laments this). Ultimately, like Jacob Taylor and Kelly Chambers, she is one of the few members of Cerberus with moral principles and standards, and that to me is an interesting character premise. Of course, I do also love how Miranda finally gets her eyes opened to the evil of Cerberus and resigns, further proof that she is nowhere near the heartless monster most members of the fandom believe her to be.
So to sum it up again: Beauty, brains, badassery, and a hidden heart of gold, plus a good character premise, good character development, and a very tragic past with a pure evil father that (to me) makes her easy to sympathize with. What more can you ask for? If I had to pick two women to save me from a bunch of giant robot squids shooting lasers, I'd definitely choose Paragon FemShep and Miranda.