It's tricky. The UK still had plenty to make it a decent place to live. Our weather is not too extreme, we are pretty free, we have lots of things we take for granted. However compared to the UK in say the late nineties up to about 2008 then yes it has declined.
The NHS has definately gone downhill. Trying to get GP appointment bit of a nightmare whereas in nineties you used to get same day appointments with a phone call. So much so I have had to start using a private GP. I avoid hospitals after reading the threads on here especially A&E. I would only go if I had a life threatening heart attack or stroke which I guess is what you are supposed to use them for anyway. The idea of waiting hours in a crowded waiting room fills me with horror. I do feel more anxious at the idea that ambulances don't always come quickly now. I have never dialed 999 before but it was comforting to know the service was there. That said part of the decline is due to people abusing the service and also the fact that the goverment has let so many people into the UK that all services can't cope not just the NHS. I think it still works for some areas but if you are moving back be prepared to pay for some services or do without. Same with dentists. I have a private one now and pay £40 per month for comprehensive covers everything insurance. The NHS needs reform and to be made a co-pay system.
Overpopulation - the country feels too crowded now and I live in Scotland outwith the main cities. For whatever the reason that they have allowed so many people to come to the UK it is now bursting at the seams. Roads are always busy, houses are too close together and thus streets are noiser. Everyone is more impatient and angry like caged rats being squashed further together. Most of us still live in good or decent quality housing but gone are the days of big rooms, big plots, privacy unless you have mega bucks. Services such as health, police have stayed the same whilst the population has grown and so of course these services are now much poorer as they are spread thin.
Crime - it does feel like shoplifting and teenagers in balaclavas on scooters are becoming a real problem. It feels intimidating and the police appear to have no power to do anything anymore. I know we had problems in the seventies/eighties when the police were viewed to have too much power but honestly it has gone too far the other way now. I also had a relationship with a front line officer and the number defending the front line is so small it is terrifying. I live in a relatively safe area so these things do not affect me too much but even so I see the effect. Housebuilders having to mix social housing in with private housing is just pulling down nice areas and in my view is a mistake.
UK finances /politics - yes this area is /has become embarrassing. I think the world is wondering what happened to 'great' Britain and how we fell this far. Without going into the reasons we seem to have short term politicians who won't make hard decisions that are required. Finances are getting worse and worse and spiralling out of control with overspending and overborrowing and rising bond rates etc. People are showing their discontent by voting reform etc and I suppose it will be interesting if not scary to see how it all ends. Working seems to be paid poorly now and claiming benefits seems to be an attractive alternative for too many.
Cost of Living - I think we had it really good for quite a while from the nineties to 2008 and now we are going back to a time more like the seventies with problems. Inflation is not as high just now but with crops failing due to weather, fertilisers shortages due to the Trump's war we are being told to expect a tough winter with shortages and increasing prices. How bad it will get nobody knows really. I still eat well but yes it costs more than it used to. Electricity/gas seems to cost alot more than say 5 years ago. I think perhaps we just didn't appreciate how good we had it before.
Unemployment - from reading the threads it seems this is becoming a problem. Certainly jobs like paper rounds and shop assistants which I had when I was young are things of the past. Thankfully I am retired now but I worry about what will happen to the state pension by the time I am due to collect it in 10 years. Lots of young people out of work and yet there seems to be so many things not getting done. Tradesmen are a nightmare to find so I hope the new govt is about to train up tons of youngsters to be tradesman.
Problems with the rest of the world - world order is definately changing. I see it with China and the US with China becoming more powerful and the US less so. Since the UK has always been tied to the US we are by defination losing our US relationship power too not to mention the fact Trump seems sick of all the support the US gives and is now expecting Europe to do more defence etc. Rightly or wrongly this puts additional strain on UK's finances although it will hopefully provide jobs for youngsters too.
Is the UK 'fucked' - well compared to many parts of the world no. We are still a relatively good place to live. However standards have definately declined in the last 10-20 years, services are not what they were, things are more expensive and people seem more angry and entitled. Make of all that what you will.