I’m from Sweden, so if I’m traveling in Europe I’m mainly taking flight to the continent, and then travel by train between countries in the continent. Must be even worse to only rely on train for the Finnish.
Always taking train between cities within Sweden, unless I’m going to a northern city like Umeå for some reason (incredibly rare for me).
I’ve only tried the ones going south (SJ to Malmö/Copenhagen and SJ and Snälltåget to Hamburg and Berlin) and have found them to be perfectly adequate. The rolling stock is old (ex-Deutsche Bahn) but refurbished, they’re mostly punctual (though running through Germany can compromise that) and offer a comfortable journey. SJ Stockholm to Berlin (leaving at around 17:30 and arriving before 9 the following day) is just about manageable, though once the Fehmarn Belt tunnel is complete, I imagine that will depart around 20:00 to arrive at the same time. Other than shortening the journey, my wishlist would be ÖBB NightJet-style single-person capsule compartments, onboard WiFi and a dining carriage (though apparently they’re working on the latter).