I was in New York then suburban New Jersey for a while so not California, but what I missed about the UK/disliked about the US was in no particular order:
pavements - my maclaren buggy packed up after 2 weeks living in the NJ dormitory town we ended up in
having to drive everywhere cos there was nowhere within walking distance
proper tasting bread (US shop-bought bread tastes weirdly sweet) and chocolate (just weird!)
the intense parochialism - even in somewhere 30 mins away from NYC I'd have people asking me "outta state?" no mate, outta country
the size of portions in restaurants and cafes
the size of quite a lot of the customers (I felt absolutely tiny - not so much of a problem in California I suspect)
yes, taxes are lower but you're paying through the nose for all those privatised services - healthcare obviously, but also things like refuse collection which came as a surprise
the amount of bodging going on when it came to public money being spent - walking down 6th Avenue surrounded by some of the most expensive real estate in the world and in order to comply with disability access requirements workmen had splodged a load of tarmac on the crossing to create a makeshift ramp
all the other mums at ds' nursery school having absolutely perfect teeth
what I liked: the space, being able to get into deep countryside in 10 minutes drive, there were bears in the hills! proper snow, proper summer, "film" rain, proper weather generally, none of the grey bleughness we have here so often, the local ice cream parlour, ds liked the flags/decorations which lots of our neighbours put up for the most spurious of reasons, Trader Joes, the colonial houses
you know, I haven't thought about most of this for ages - it's all coming flooding back