To start with, this is not just Pendragon's best by a long way, it also has to be one of the best rock albums of the last 20 years. It's still recognisably Pendragon, just about, but with the worst of the 'folky' bits stripped out and replaced with Rammstein-esque ear-bashing. It's rather more 'rock' than 'prog', so it may not be to everyone's taste, but for me it's the 21st century makeover that's been long overdue in the prog rock scene (credit too in this regard to IQ, whose 'Frequency' also fits the bill).
To finish, a genuinely excellent album, one of those ones which you end up listening to so often that you think you can't face hearing it again, but then you put it on and end up listening right to the end all over again. The only downside is that 'Pure' sets the bar so high, the next one's bound to be a disappointment!