Every release up until Immortal Pride expressed a distinct combination of concept and aesthetic, whereas the later albums could be categorized into "mini-eras", in which Darken tried with varying success to find the best voice for the ideas to be conveyed.
Immortal Pride, Creed of Iron -> 10 minutes of Poledouris per song, compositions veering into "synthesized classical" territory (with lots of phat breakbeats on CoI).
Memory and Destiny, The Fire of Awakening, Dawn of Iron Blades -> tighter songs, presenting motifs to expand upon melodically/structurally instead of expanding ambience.
Fire Chariot of Destruction -> twangy guitarwork reminiscent of FtVoB, arguably a return to the thick ambient layering of Thousand Swords; recapitulated quite a lot of themes from the previous three releases in a new context. I'd say it expresses a sort of ferocity that the other late Graveland lacked and still lacks.
Will Stronger Than Death, Britney Spears of Destiny -> a merger of Darken's current repetitive instrumental style with Lord WInd's meditative approach, which is kind of like sitting before an ancient temple all day and paying attention to the rhythm of people flowing in and out, calves slaughtered on the altar, etc.
The future -> another Fire Chariot of sorts would do, restating what was done up to this point, but with a more conscious use of disparate stylistic implements, i.e. not constantly drowning out majestic themes with Atlantean Valkyrie Choirs, which themselves would benefit from an overhaul towards something more akin to medieval polyphony.