Jack Wall first and foremost.
The ME1 soundtrack underscored the sci-fi feeling perfectly! Absolutely love it to bits and it is way more impactful and memorable than the music from ME2 and ME3 (though the ME3 score gets points for at least wanted to get a bit closer to the ME1 synth style at times) which for the most part just feels like the same generic blockbuster music. I've heard so much Two Steps From Hell, etc. that all that kind of theatrical stuff just blends into one blob of music you hear at every corner. The music is good, but we're getting oversaturated by it in every other trailer, game, series and movie. It's simply nothing special anymore.
Though I do like the idea of Yoko Kanno that was tossed in here. I don't think I ever heard a track from her that I didn't love.