I'll have to dissagree with some of you, I though she looked like she was very overwhelmed, and she had been crying.
And I know you can say she may had been tired, but still I would have thought she would look more radiant and happy. I felt sorry for her. Now is when a marriage is going to put under stress, I don't know if there marriage will be able to handle it. This is my IMO.
I thought exactly the same. I figured that this moment was probably the most vulnerable in her life; literally hours after giving birth to her first baby, exhausted, and she's probably never been so stalked, and she still has to look amazing. In the heat. Which she did, of course. Overwhelmed would be putting it mildly! Friends of mine I saw in the hospital in the same time frame that she left the hospital were swearing that they've 'shut up shop' so to speak and will never go through another labour again (which of course wasn't the case).
William looks wonderfully relaxed, as did the grandparents, so the tension doesn't seem to be more than expected. Apparently there were hundreds more onlookers and press for Baby Cambridge than William.
Meanwhile, I love how seriously cuffed QEII looked! Her face and smile we're beyond priceless. She does florals like no one else.