Well, don't get Isle of men or 3*7, both are collections of songs, and really for fans, and one of the great things about the band is that they write albums, as opposed to a collection of songs (well, it feels that way, anyway).
I don't have HEart, so I'd reccommend Omnio, it's a fucking great album (and when I say great, I actually mean 'great'). Strange in Stereo is cool too, but Omnio would be a better starting point.
Omnio is black metal, in sofar as the approach to some of the guitar parts (high pitch, speed picked riffs, in places), but it's completely lacking in aggression, instead it's just a laid back, progressive, doomy psychedelic trip. Great atmosphere, emotional vocals, some beautiful guitar riffs, everything about it's fucking great.
[edit] oh, and it has alot of that twin-guitar type approach (kind of) of early Opeth, but taken to the extreme- the parts quite often have no relevance to each other, it seems like each guitarist is going off on their own journey, but the combination is stunning. So many layers to it aswell, I can still hear something new each time I listen to it, and I got it when it came out (however many years ago that is, quite a while)