I'd probably give my notice in at work, and take some time to consider if I'd want to do the same job on a flexible/part time basis (possible) or do something totally different. In the long term I would want to keep doing SOME sort of work activity.
I'd buy a big family house for me and DP and part-time DSS close to where DSS lives most of the time with his mum, in the suburbs.
I'd buy a little apartment in the main city near where we live for use on weekends and late nights out.
I'd buy a little apartment in London for when I go back there to visit my friends there, and I'd be able to use the money to buy unlimited last-minute train and plane tickets to visit my friends and family in the UK which would be the best thing ever (I live abroad, not far, but not easy to get to UK cheaply without booking everything months in advance)
I'd buy a new top-of-the-line instrument that I play to replace my old knackered one, and also a piano.
I'd buy DP an Audi
I'd make my mum retire immediately and buy her a house near where her sister lives, I know she wants to move there.
I'd sit down and do some serious caluclating and organising to work out how much money to give to which friends and family, and also what lovely gifts I could get them all in addition to just cash injections.
Also calculate and work out how much to give to which charities
I'd seriously think about getting a dog, but would need to work out how the money could overcome some of the practical issues