Jack is just so damn cool. I mean, look at her! She doesn’t give anyone the time of day, and her tattoos are very elaborate, and tell a story. Her loyalty mission was powerful, and her dialog fits her character very well. In Mass Effect 3 she blossomed into a much more mature person, truly putting her life lessons and experiences she had with Shepard in Mass Effect 2 to good use; going to the Grissom Academy and teaching kids how to control their biotics is far beyond any expectations I had for Jack after Mass Effect 2.
This gave me a lot of new appreciation for Jack, and quite frankly, I really like her hair in the third one, too. She’s not afraid to call Shepard on his/her shit, either, and it kinda adds to her attractiveness.
As a squad member: I used her very little.. She was a bit disappointing. The story made her out to be this Godlike powerful biotic, when in fact she was just another Adept.