One thing I've noticed is that if you're willing to live a bit outside of a major city and along a commuter rail line (a commute not extraordinary by U.S. standards but seemingly insane by European), housing costs can be much much lower.
With a few exceptions, the kind of tech work will likely be more prosaic in nature. The kind of big startup scene you might find in SV or other places in the U.S. does exist in Europe, but not at anywhere near the scale or with the kind of capital availability that's present in the U.S. On the upside, the work tends to be very stable.
Long-term, you'll have to think about retirement and either make a decision to stay or return and start saving up. If you come back to the U.S., the system is designed to offer you a reasonable retirement, but only after decades of saving. You may not think that's important at 26, but you'll likely start to feel it at 36. If you stay in Europe, you'll need to figure out the local retirement system and how that work.
If you pull that trigger and stay in Europe, you'll probably want to look at giving up your U.S. citizenship because you'll be obligated to pay taxes the entire time you're in Europe (there's some deductions, but you'll still have to do all the paperwork).