The Best Original Score category tends to favor established composers over newcomers or those never nominated, to the point where it seems like it's an exclusive club. John Williams - the Meryl Streep of composers - seems to be nominated more or less every time he works, to date racking up 44 nominations in this category alone (he also has a handful of Best Original Song nods, bringing his total to 49). Alexandre Desplat has been nominated eight times in the last eight years, including two nominations this year alone for both The Imitation Game and The Grand Budapest Hotel.
However, that trend has been slowly changing over the past few years. The past four winners in this category did so on their first nomination, and each of the past 11 winners did so on either their first or second nomination. In fact, the two of this year's nominated composers hadn't been nominated before: Gary Yershon (Mr. Turner), who's scored each of director Mike Leigh's last three films, but otherwise only has a few television credits to his name, and Johann Johannsson (The Theory of Everything), who's most notable work to date had been the score for Prisoners (2013) but has been making music in his native Iceland for years. And as of this writing, Johannsson is widely considered the favorite, making it possible that this streak could be extended to 12 years running.
That being said, the best score in this category comes from a composer who has been nominated 10 times before and has won once before: Hans Zimmer's score for Interstellar. It's a massive work, both sonically and ambitiously. The most distinctive feature of this score is its use of organ, an antiquated instrument that's now mostly relegated to old churches (in fact, the organ used in the score was recorded at London's Temple Church). It's an odd mix, to have such an ancient instrument woven into a score featuring synthesizers and a full orchestra. Yet it works perfectly, and not just because the results are aurally excellent. The organ works within the film's main theme as well: humanity being the core of technology, not the other way around. The organ brings warmth and emotion to the score; no matter how epically the music swells, it's never less than human.
In a featurette published on Slate last November, director Christopher Nolan notes that he had wanted "religiosity" in the score for Interstellar. The organ certainly provides that, and the score itself can feel like a religious experience in and of itself. It can feel like it spans the entire length of the universe, yet it never loses its beating heart.