From ARN to ORD you're pretty much guaranteed to fly the new cabin which is a major upgrade from the old one. The new timing of the flight also makes immigration a breeze. In general service on SK is terrible, but it is highly crew dependent. The higher the average age of the FA's the worse the service to the point of being ignored and insulted (this is a fact, not a joke).

Since your profile doesn't list a location I can't tell wether you're Scandinavian/Finnish. If you are, then the only thing to keep in mind is that the IFE is of good quality but with a very limited inventory and if you watch movies on a regular basis you'll probably want to bring some entertainment yourself. Also if you're Scandinavian/Finnish you can probably tolerate the horrible food SK tends to serve in the outbound direction. If not, have something to eat at the airport before your flight, just in case.

I do a considerable amount of longhaul flying with SK, the pro's are the new cabin and general product, the fact the flights are generally on time and the very small amount of administrative/ticketing bs I encounter with them. The conns are the food, lack of service and limited IFE. While disappointing I can mitigate the last item, the first two are for SK to fix.