Lots about this already in other comment threads, but a first hand experience to share here.
Let's cut to the chase: if you're in tech, and you're any good at what you do (you know who you are), you likely shouldn't waste your time on Helsinki or anywhere in Europe.
Let's start with the money...
In Helsinki as a software engineer you're looking at 3kEUR - 7kEUR monthly salary before tax. Only the flashiest software consulting firms will pay ultra senior people 6k (you'd better have 10+ years of experience to even broach the topic!). In Finland, if you make 6 kEUR a month you've "made it" and your colleagues will be openly jealous (yes, really). Stock options in Finland are a joke, you will receive perhaps a tenth of what you might anywhere in the US (if even), and they will be non-qualified options in American terms, there is no such thing as an ISO here.
Taxes? Your all-in income tax will be 40-50% on that 6k income. Plus 24% VAT on anything you buy in a store. And as a completely medieval twist, food is exorbitantly expensive in Finland because the "reduced" VAT on that is 17% (by comparison in most civilized countries groceries are taxed at like... 1-2% if at all).
If you want to convert what that means to SF terms, using the last year's USD/EUR FX rate and some cost of living stats from Numbeo, you'll find that you can multiply a Helsinki monthly salary in Euros by 12.5 and then again by 2.02 to arrive at a yearly USD salary in SF equivalent (there is a quirk about vacation money in Finland, hence the 12.5 instead of 12 months).
So the Finnish tech pay scale scales to.... 75kUSD - 150kUSD if you were in SF, given FX and Cost of Living adjustments outlined above *
In SF you're looking at 100kUSD - 250kUSD per year, and lower taxes across the board, realistically. In SF if you agree to a 120-150k salary, you're either quite early in your career or are one of the first employees at the company and receiving a handsome options grant. (and again, in Finland, you won't get nearly the same options, think missing-a-zero territory, really).
Which brings us to our second point. Talent pool and work ethic.
I've spent the last couple years hiring in tech extensively in Helsinki. I know the talent pool reasonably well. There are certainly some diamonds in the rough but on the whole it's very weak.
Anyone who can get a job in the US has already done so and left, not just because of the massive economic incentive, but also because A-players want to work with other A-players. Smart motivated people want to work with other smart motivated people. The best want to learn from the best. It's as simple as that.
Most of the people you'll work with in Finland are very nice, but more than a few are also keeping detailed records of their contractual 15 minute coffee breaks. It's a "punch in. do work. punch out." kinda place on the whole. There are obviously exceptions and I am exaggerating a bit to get the point across, but the overall vibe is that going the extra mile is rare and frowned upon (you wouldn't want to make everyone else look bad!).
The same work ethic issues seem to apply to founders, who are often all too happy to put the brakes on their company to take a monthlong vacation in the summer. While that's great for work-life balance it's just not business smart if you're trying to get a startup off the ground.
On the other hand, is it a nice place to live? Yes, yes it is. Stuff just works. You're not accosted by homeless people on your way in every day. You get the sense that perhaps those taxes are actually buying something useful and relevant.