Josef Altersberger's soundtrack was different and darker, but I liked it too.
Oh, and I have another suggestion and I told about it before in another thread: trading cards.
I've seen many developers add them to their games. Like Serious Sam 3 and so on. Achievements, on the other hand, aren't really necessary.
I hope that the story will be dark, too. Shadow of the Phoenix was sort of dark, but with the Nameless and darker kind of music by Josef Altersberger would really make a special kind of a feel, I think, so I hope you can make it!
(Maybe the Gods in Spellforce can die and the mortal races are left alone under the protective remnants of Aonir's lights!)