You seem to be asking about the relationship between happiness and FIRE.
People with more money tend to be somewhat happier than people with less money - but this diminishes as you go above the average money for that society. People tend to be happiest when they are very young and very old - and are most miserable when they are in their 30s and 40s. People tend not to change happiness much (apart from this curve).
However, if you have a gratitude journal, exercise, take notice of your surroundings you can become much happier. MMM seems to have done all those things as a result of FIRE, and he encourages other people to practice them. In a sense, the blog is MMMs gratitude journal. He encourages us to think before we buy - that means that we effectively become grateful of any purchase, and take much more notice of our surroundings. He also encourages us to exercise more. By living a frugal lifestyle, we effectively have more money than our peers. All these things probably make us happier.
In answer to your question - yes I am much happier since I FIREd, and it is better than I expected. I expected it to be pretty much the same, just without the hassles of work, so I guess my expectations weren't that high. However, each morning, I can appreciate the sunrise and how beautiful the valley below looks - and I appreciate that I can do this every day. When it is miserable outside, I appreciate that I don't NEED to go somewhere in the current weather. When it is nice (even for only a few minutes) I can take advantage of it, and go outside to do things. Things don't NEED to be done today - there is always tomorrow. This all gives me a deep satisfaction that I didn't anticipate. My father has cancer and my parents live far away. I can visit them whenever I want, without the conflicts that work would give - this also makes me much happier. These are all simple things, but they are available to me in FIRE, and weren't before. I think happiness is based on simple things.
