The only differences in Swampsongs sound that I noticed are:
1.) Antti seems to be using wah on some tracks. It seems that every band out there is using this effect but Antti really knows how to use it to benefit the band.This can be used to achieve a more "Melodic" sound.
2.) All the tracks off of Swampsong are a hell of a lot more aggressive. No doubt about it. They keep the harmony, add the aggression, and further pursue the style that is Kalmah.
3.) They are better musicians now. They have the practice and experience under their belts to really show us what they can do.