A matter of taste, of course, but I find that most Finnish music sucks ass.
I listen to some Finnish rock (CMX, Viikate, Maj Karma, T.R. & Trio Niskalaukaus, etc.), though, but mostly for the lyrics. Musically they're often very basic and boring.
Magyar Posse, Shogun Kunitoki and Callisto are most frequently on my playlist out of all Finnish bands, but are really an acquired taste, I think. Kingston Wall probably deserves a mention, and a really underappreciated band is Hidria Spacefolk.
As for Finnish metal, I find it mostly overrated. It's soulless and dickless and very very basic (talented musicians for sure, but no creativity). Then again, that's what most metal is anyway. Most, but not all. The exceptional ones don't come from Finland, though.
Finnish rap is a bad joke. I used to laugh, now it just makes me cry. Well, not really. I just ignore it.