Watson: I love Lucy Liu. Just need to say that again. She's clearly broken. She was the head of her class at med school, she was a surgeon, and she had a patient die due to something that was her fault.

What is sort of hinted about is family and ethnicity: She has parents, who are alive, around, and fairly well off. Certainly well off enough that she could move home if she wanted to. And she's asian. There is a whole layer of interesting social things they could and might do regarding the fact that she's now possibly the disappointment of a high achieving family. Ethnicity doesn't always apply- being the disappointment of a high achieving family happens across them, but in the context of such things as the "asian f", and "model minority" status, there might be a new story here.

Joan is a professional. She's interested, but she also has boundaries. Defined boundaries, and will not be drawn into these shennigans beyond her comfort zone. At one point in her life, she clearly had her shit super together. And now, not so much.

Boundaries: Another contrast to BBC. BBC Watson basically marries his Sherlock in 12 hours of knowing him, sealing the deal with a justifiable homicide. Joan Watson turned Sherlock into the police for destroying her car. Unlikely to murder some one for him until at least the second season. Boundaries are good.

Parents: Both Joan and Sherlock have them. Which isn't actually surprising for a pair of 40 year olds in 2012. Not something addressed in the ACD stories for all sorts of reasons. BBC has avoided mention beyond Mummy, and has Mycroft standing in loco parentis for basically everyone instead.

Deus ex Mycroftia: Something tells me that the solution to everything on Elementary isn't going to be "call my creepy CCTV obsessed brother to get it fixed". In a 22 episode season, this is only for the best. Otherwise you run the risk of them turning into Mycroft's angels, saving the world on call.

Also, the whole "i am the government" doesn't work as well in an American context. It really doesn't work with a UK Mycroft and a Sherlock in NYC.

Irene Adler: I hope she shows up, she is awesome, and she is not a dominatrix. The very fact that Sherlock has a visit from one in the first ep means that her profession is less likely to enthrall him.

Finally, as I have to go to bed, a fic prediction:

There were be so much sub Sherlock BDSM porn written about this series that you cannot possibly imagine. It's going to be a go to series for femdom stuff. And it's going to be full of crossovers in which every single dude ever ties Sherlock up and has his way with him.

(Or there will be a lot of Gregson/Holmes, ignoring 'hot hispanic cop/Holmes' entirely)

It's going to be so heavily weighted sub Sherlock that people will be begging for him as a dom. Expect honey to frequently feature.

Even better, you are going to see it hit the omegaverse stuff when it gets written. Which it will. I predict a 70/30 split of Omega!Sherlock to Alpha!Sherlock.