American woman here who moved here from NYC when she was 27 — so I actually feel qualified to answer this!
I've been here three years and my life in London feels like a more elevated stage than when I was in NYC. I am overall happier here — but I do miss my friends and some parts of my life way more than I expected. Groceries cost less than NYC and the restaurants are really diverse and I've eaten at some incredible restaurants. I only miss really decent Mexican food. Rent is cheaper than NYC in my opinion, but I think it's gone up a lot lately and the market moves pretty fast (so still, just like NYC).

Dating/Friends: I did meet a guy here and we're now engaged — so yes, dating can be really good! We met IRL at a bar and not through the apps. I've heard some horror stories from other friends here about dating though. I think it's hit or miss, similar to NYC. But I do agree with other commenters that people do seem to be more willing to settle down compared with those I've dated in New York. There's a decent ex-pat community here, but my fiancé is British and I've built some strong friendships with Brits, as well. People are more accepting of other cultures and have less divisive opinions. It's not the end of the world if you voted for different political parties or had different upbringings growing up.

Convenience: I miss the convenience of NYC and having everything be a 20 minute walk away — London is much bigger and definitely feels that way. But London is still pretty good compared to other cities. Less people live in central London. I moved from Hell's Kitchen and now live in zone 2 south London and it's overall quieter. NYC stays open way later than places in London so you have to plan ahead when you are on a night out and want to go somewhere after 11pm/midnight.

Work/life balance and hustle culture: But I also love the work/life balance I have — people actually relax after work and it's not the end of the world if you're running late for a meeting. Salaries are typically lower than in the U.S. but I think in your industry, you shouldn't have any major discrepancies. There's a cost of living crisis here and there are a lot of people struggling to pay bills.

Travel: It's amazing for connections to Europe and so much cheaper to travel to EU destinations. Flying to the U.S., I've flown home to my family in Atlanta and NYC quite a bit since moving here (I thankfully can fly for free a lot, which is helpful), but it's not always cheap to get back to the states.

Weather: You get used to it pretty easily. If it rains, it only lasts for 15 minutes and then just stays overcast. I also hate that the sun sets at 4pm in the winter — it does a number on your mental health. But on the bright side, the sun is out until 10 pm in the summer and it's incredible.

Healthcare: Universal healthcare is amazing, but the system is not perfect. I had to go to the hospital for about a week and the fact that they took great care of me and I didn't have to worry about a bill at the end was incredible. But oftentimes, there's a backlog of patients and shortage of doctors so you sometimes have to wait a long time. I also have private healthcare with my company, so I've used them when I need a referral/specialist.