My effective tax rate in London with a salary slightly higher than the OP was 38%.

My effective tax rate in San Francisco with a salary 4x what I was making in London is 36%.

Rent is comparable, with bigger appartments in San Francisco, buying is comparable. Quality food is more expensive in SF, other goods (electronics/clothing/etc.) is more expensive everywhere in Europe. Quality of life depends on wether you like the outdoors (SF), want a car (SF), or prefer city activities and/or dislike driving (London). London is also great if you like to travel, specially throughout Europe. The West Coast is particularly far from almost everywhere and there's a distinct lack of cheap airlines. From London you can have a $20 weekend getaway to, say, Prague. Admitedly, you do travel like cattle, but it is cheap.

In the US, besides what you're taxed, you must add all other fees that get added to almost anything you'll want to do, from healthcare to going out (the famous tipping), going through bank transfers (they're free throughout Europe, regulated markets, they charge you whatever the bank wants to in the US, only reliable way to transfer money here is to send cheques).

Overall, myself and my wife like it here, have made some great friends and don't really want to go (wouldn't cry for too long if we had to). We can save a ton of money because we have two incomes and weren't looking for the "2.5 kids house with garage for two cars and white picket fence", so we got a deal on both appartment ("small" for american standards, twice as big as our flat in London for roughly the same ammonut before the pound plummeted) and our car ("tiny" for american standards and manual transmission, it cost less than the anual insurance).

Every place is great to visit, every single place has things you'll complain about when you move there. Honestly, the thing that worries me is political, from the madman in power to the old lady that screamed at me and a bunch of other techies that "Trump won now so y'all will have to go back, I'm getting my city back." I didn't see the fallout from Brexit, but from my friends over there it is not as bad as here, but objectively bad regardless...

It's banded in the UK. Your first £11.5K of income is tax free, the balance up to £45K is taxed at 20%, anything over £45K and under £150K is taxed at 40% and anything beyond £150K is taxed at 45%.

In return you get free education up to (but not including) university age and universally free health care.

There's also national insurance at 12% of earnings over £680/month (money from this tax is used to fund state pensions and unemployment benefits).

It's 40% on earnings above around 45K, below that it's 20%

This is pretty common in Europe. For example income tax and social insurance contributions in Ireland would be greater than 50% of marginal income at this level. This money is used to fund services and fund the national debt.

Personally I'm quite comfortable with it even though I'm in that bracket.

Someone earning his salary is taking home £36k or so, paying effectively 28%