Wow... just wonderful, David Hockneys A Bigger Picture is well worth a visit. It was so good it filled the main part of the Royal Academy. The digital part of the exhibit was suprising - I did not think I would enjoy it as much as I did, it drew you in.
Also a mention to the RA - the first tickets sold out so quickly but their Facebook page had a link for Eventim where I finally got tickets for a very good price.