Interesting that you moved from California but do not comment about the London sun at all, though to be fair, you said you yourself moved to Europe and not the UK.

A friend from SoCal who moved to London for a few years couldn't really handle sky getting dark around 3-4 in the afternoon in the winter, and she would say it was almost impossible for her not to get depressed during those times. So just something to be prepared for.

On the bright side though, London, as with many German cities, has short cheap direct flights to many sun bleached cities and beach destinations in Europe so I would suggest making ample use of them if you can. Being in the US afterwards, one realizes there is no location in the mainland US that can compete with the Mediterranean with respect to actually being an inviting body of water to swim in (non mainland Hawaii is obviously an exception).

And May and June in London itself I often find especially beautiful as well.