I've done this many times. Normally the roads are in good conditions. After heavy snowfall the preparation of the roads is done fairly quickly. But the roads are often covered with ice, especially in the northern parts of Sweden. Since all Swedish cars have studded winter-tires this is not a big problem and if you get a rental car you will have studded tires too.
You just have to realize that the breaking distance is still much longer than on dry roads. This can be problem with sudden encounters of elk and reindeer. The only criticaly situation I ever had in Sweden was when I was driving around a curve with nearly 90 km/h and suddenly 10 reindeer where standing on the road in front of my. Luckily I managed to drive around them without hitting any of them.
If you have at least some experience driving on snow don't be scared to drive in Sweden. What I would recommend is taking a warm sleeping bag for emergencies. If you have an accident with you car it could take a couple of hours until another car arrives and at -35°C outside temperature this can get dangerous without something to stay warm.
I can only endorse what Boris said. We drove from Kiruna through Abisko to Tromso after a night of shooting. The weather was mad with heavy snow storm but even at 4 am the snow ploughs were out and driving was no issue.
Warm stuff and water is a must though (and keep the water near the radiator as we learned when it froze on the back seat ).