Eileen's personality attracted me to her. She's sweet and nice and cares about pretty much anyone. And I mean that wholly!
[On a side note, she can swing a nightstick like a mo-fo. :P]

I loved the chemistry between her and Henry... I also was very touched during the short scene where he comes across her medical charts & ex-rays/pictures on the whiteboard in the Hospital world... Aww...
At first, I was a little skeptical about this Maria-style tag-along, but after I figured out you could give her weapons of her own, I soon changed my mind. Does she ever deal out the pain when she herself is injured.