Necropole play a very tense style of orthodox black metal driven by fast-changing melodies contrasted by a slower-changing root. It's all about tension in ther air, an endless stasis of eerie, menacing discord. Their style is very similar to Sargeist, though Necropole use two guitars, which pairs the contrast of melody and dissonance differently.
Nearly the whole running time adheres to this orthodoxy of the same tremolo patterns holding a static tension. Each song starts with a blast beat section, slows it to a back beat, then repeats. The exception is the bridge of "Trahison fratricide" which progresses nicely with a dual-tremolo harmony over double bass. Ironically, it is the shortest song which progresses the most. Despite the ever-shifting guitar parts, only one song really goes anywhere - everything is framed within the fairly strict adherence to patterns. Tension isn't built up and released, it is the unrelenting mood of Ostara. The melodies are merely a feature of the soundscape, not themes which guide you through the experience.
To once again compare Necropole to Sargeist, the tension patterns on Let the Devil In were longer, more pronounced, and drawn out. The tracks were shorter and the buildup and release of tension much more grand. Necropole's songs flow smoothly, but don't really go anywhere, a contrast to the typical dissonant French style which has an abrupt and jarring flow which escapes resolution with sharp turns.
Ostara has an enjoyable atmosphere and aesthetic, but aimless and unfulfilling songwriting that fails to complete the experience.