Lived in london for over 40 yrs, from late teens till recently. Not smack bang in centre, 25 mins on train.
Big cities will always have "issues" and you either like it and go with it, or not. Where I lived (Enfield Town) it was generally ok, but in recent years the general atmosphere changed. The citre centre "edge" was moving outwards and we didn't like it, getting old. House prices had gone nicely stupid, so we sold up and moved over 200 miles away. Financially London had been great for us (Thanks London !). Absolutely no regrets, even though the house that we sold continued to increase in value, enormously.
Still go back occasionally, sometimes even just for the day by train (450 mile round trip). I agree with Lizzie, it's easy to be negative, but it's been worse, and still could be much worse. Proportionally, I see just as many junkies begging on the streets in Swansea as in London.