Mia is one of my favorite dolls. (I still can't choose between her and #25, but Mia was my favorite for several months before #25 arrived!) I love the hazel eyes and the unique freckle pattern. The layered hair and the zigzag part can become really frustrating when you're trying to do braids and certain other styles, but I would never trade it for anything. The hair is a really nice strawberry blonde color, although it looks red in certain lights/pictures. She has the same decal eyes as JLY#21, and they are absolutely my favorite eyes! They're gorgeous, and look just right with Mia's hair color and freckles. I have not noticed that my Mia is any chubbier than any of my other dolls (she is kinda fat, but in truth, all AGs are...).
Honestly, half the money I paid for her, I was paying to get my hands on her adorable meet outfit. I just love it! As Keri noted, the jersey skirt she comes in is very hard to get off. There is no velcro, and very little or no elastic in the waistband. I found that you CAN do it, even on a PM girl, if you wiggle it just right, but it can be a pain. I absolutely love Mia's meet shoes! The purple laces make it really unique. Also, I like the elastic "laces", because lacing up dolly shoes can become very irritating. As for her shirt, I loved it so much I ended up buying it in a girl's size for myself. I haven't had any problems with the decals coming off, and I just adore the thumbholes.
A+ for Mia! She's really pretty, looks good in almost every outfit, is very unique compared to other dolls, and is just all-around awesome.
One last plus for Mia is that her books are very well-written, and I really enjoyed reading and re-reading them. Probably my favorite GOTY books!