Well, it's hard to freely speak my mind about the Brits w/o getting downvoted, but they created a large problem and let their dogs out on whoever complains about it.
Ireland is solid, especially for any sort of biotech/medical. Strong critical skills immigration path, good wages, pretty much every major company has a facility there (many rivaling the US sites in size), friendly and welcoming place. Housing is a bit of struggle, mainly for renters.
Irish infra is not great if you compare it to many advanced European countries. I hate they still do not have a train/tram connection from the airport to the city. Taxes also make you weep. Not to mention an immense risk of losing all those corp taxes and industry if US pushes ahead and creates barriers for companies to trade. It is great at many things but also has some downsides.
It wasn't terribly difficult, you just have to find a company to hire you. Weirdly the biggest issue I ran into was companies not believing I was willing to relocate and assumed I was just some idiot looking for a remote role. The paragraph about it in my cover letter didn't seem to matter.
Apparently I was initially rejected for that reason, but my boss dug me out of the file for a potential discussion about a US based role. He told me that 6 months later over pints.
Once you've got an offer the critical skills employment permit (CSEP) is quick and painless.
All in all it was basically a lateral move lifestyle-wise. "Federal" income taxes are high-ish, but there isn't another level of state and local taxes eating away more; and property taxes are practically nonexistent (€280/year I think?). There are a handful of schemes which will shield a decent chunk of income from the highest tax rates, and the company benefits are fantastic (medical 100% paid for for my entire family, good bonus, 2:1 "401k" match).
As mentioned, housing is absolutely horrible right now, especially for renters. Luckily home prices are still somewhat reasonable compared to the US - we made enough selling our US home that we could buy an Irish property outright. Can't get a mortgage or any sort of credit until you've been in the country for 6 months. Probably won't stay in this place more than 2 years (when I get permanent residence on the CSEP route) but its a comfortable enough spot to get settled.
I wish it was a bit less car-focused, but there will be a train that drops me off basically at my office door in ~2 years, so they're trying and improving pretty quickly.