If Lars was tired of touring in the band and wanted to step down, then I'm glad he did. If one is not happy with the way things are going, one should change it, regardless of if the fans are sad. He was a great drummer for the band, but life changes things and sometimes people find something more important, especially if one has kids.
As far as Horgh goes, if Peter really needed to get another drummer, this was his best choice I think. Especially considering the many times Horgh has played/toured with Peter, especially in Pain, and they get along very well. Pain has no blast beats whatsoever, so I don't see that being a problem with the Hyopcrisy tunes. Also, Horgh went into Immortal with no black metal-playing background... he played traditional heavy metal. He is quite versatile. If you listen to his newer band, Grimfist, you will hear the same thing. Some blast beats, some old-school metal drumming. But if Peter wants to try putting a few blastbeats in the Hypocrisy tunes, I guess we'll see next month what that ends up sounding like.