I'd really have to disagree with you there! I've lived in Bristol for 4 years, having previously spent 8 years in London - people are I know are happy here and find it difficult to leave. I've never lived in such an uplifting, diverse, creative place as I do now (Easton, BS5).
Also worth mentioning (response to a comment above) that there's a lot of colourful houses and murals all over the city, not just on the bits you see on postcards...!
As a foreigner, Bristolians were the most congenial and welcoming neighbours I have had through out my time in the UK, and I moved around a fair bit in the past decades.
I still have very good friends (and memories) in Bristol.
Nothing but positive things to say from the city and from big hearted Bristolians. Like you say there really is a positive energy about the place. Truly gert lush!
Also worth mentioning (response to a comment above) that there's a lot of colourful houses and murals all over the city, not just on the bits you see on postcards...!