Well
Spain is 10 years if you're not from a former spanish colony.
Portugal does the same 10 years (except 6 if brazilians), or 3 years if married to a portuguese
Germany is 8 + need to speak German (so you might think this is difficult, but if you've lived in germany 8 years chances are you speak some good german)
French is 5 years + speak french at some degree.
I don't think these requisites are that 'hard' compared to the US. In fact, in most countries of Europe there are well established residency programs, either through points or straightforward job offer residencies. The US immigration system is complete bullshit and at the sole discretion of the NVC (national visa center).
For the US are several pathways to a Green Card: Through job or family.
Through a job, you can get a EB class green card, which is for 'advanced' degrees (people with PhDs or masters, published, and known), there's also EB1 which is for pretty much 'Nobel' level scientists and Olympians.
Through a family, it's gotta be a family member, and depending on their level to you, so a brother of a citizen has to wait at least 12 years before he can get a green card (yes, 12 years at least).
The rest, there are several 'visas' that are NON IMMIGRANT (meaning, not permanent) and allows the person to work for a certain time; the most 'famous' ones are the H1-B visas. I once applied for one; there's a cap of 65k a year, and by the third or fourth day of the reception being open, there are around 120k applications. They all get pooled into a lottery. I wasn't selected heh. The H1-B visas last for 3 years with a ONE time extension of another 3 years, so for a total of 6.
That's pretty much it, in the EB categories everything is subjective to what the official at NVC thinks of the application, if it thinks it's not strong enough he can issue a RFE (request for evidence) and pretty much close the case if he wants to.
Now take for example Canadian, UK and Australian: There's the usual family and job offer visas (in most cases, those job offer visas don't have a cap). But there's also something like 'Self-residency' where there's a set amount of 'points' say, in Canadian is 67. Then you answer a questionnaire and send evidence of achieving 67 points or more, categories are things like, education (GED, Bachelor, master, etc), job experience (3, 5, 10 years), language skills (measured by say IELTS or TOEFL), age (people 25-40 usually take the most points). If you have the points ore more, then you can send the paperwork and can get a 'green card' for said country. I did it for Canada and moved to Toronto for a few years, became a Canadian citizen then moved to the US.
I think that point process is very modern and very objective; it's clear cut if you can make it or not, and it brings the best type of immigrants to the country. That's why I say the US system is total crap.