LONDONERS is Saint John's Wood a 'high profile' area to live?

Someone I know is moving there. It looks pretty nice from what I’ve gathered online. I’ll be visiting them a whole lot.
Just curious about the area itself. Is it expensive? Good neighbourhoods? Anyone live there/been there, as personal experiences from you lovely people seem a lot more reliable than Wikipedia…
I know Regent’s Park is in the area.
Just anything you can tell me about it, even how clean the streets are or arent… anything! Thanks.