We returned to Aus after 15 years living in the UK, which was a real wrench for me because of how much I loved living there. I'm a bit of a history nerd and I'd always get a buzz about being so close to everything interesting in the world. Australia literally is at the arse-end of the world and you don't get things like cheap Amazon, next day delivery, lots of shopping choices and decent sausages! 
Also, the UK is where I've lived my entire "adult life" so it's been quite an adjustment coming back, just with knowing small things like what medicine to buy for the kids.
Coming back here, honestly, has been perfectly fine. DH is British and he finds absolutely everything here to be so amazing and wonderful and like being on holiday, whereas I'm more of the "meh" opinion. 
Our decision came down purely to providing a better experience for our two DC, who were approaching school age. For that reason alone, I have no regrets whatsoever. We had a great school and they're flourishing. We just would not have got that in London.
It's been strange to come back. So much has changed, yet so much has stayed exactly the same. People don't move on really. They stay put right where you left them. Hehe. They are all happily walking the same streets where they grew up, and have nothing interesting to impart other than the new roadworks going on down at xyz street. They also have absolutely no interest in any of your experiences. Whatsoever. It's sad really.
Since I moved in the days prior to Facebook et al, I didn't really come back to an established group of friends/former colleagues. The 2 that I kept in contact with now live in Melbourne and UK, so that's no help. I've honestly found it difficult to "break in" to friendship groups. I've kind of made friends with some parents from school, but they all have their own preferred long established groups and I'm a bit peripheral to be honest. The ones I have come closest to are actually Kiwis and Brits. The ones who've venture out a bit and are a bit more welcoming to strangers. Go figure.