I think you should get the albums in chronological order if you can. The first three ("Borknagar", "The Olden Domain" and "The Archaic Course") are their best albums and you should probably start there. From the other two I believe Quintessence is the best.I've heard both bad and good comments about the last one so you may want to leave that last.
If you liked The Genuine Pulse, then get that album (Empiricism). It's a really good album IMHO, not my favourite of theirs (that would be Olden Domain), but still very good (2nd on my list)
well it's difficult to say which album is the best to start with. I only have Quintessence and Empiricism, but I also know The Olden Domain. However, I think they're all very good. Empiricism is one of my favorite albums of 2001.