Personally I think noone should have been hired to score MoS.....the John Williams score is the end all-be all of Superman scores. It should be the standard for anything Superman related.
Believe me, I don't think anyone was more disappointed than I was to hear that Williams' music wouldn't be in this movie. I'm in my 30's and grew up with Reeve as my hero, and whenever I'd imagine him, I always heard the classic theme in my head.
But I've come to realize that this is a new Superman - the Superman of 2013, not 1978.... and he needs new music. I saw a youtube video of MOS footage with Williams' music played over it and it totally does not work.
I think the important thing about the music is that it feels like the Superman it represents, and Zimmer's score does that amazingly well.
There seems to be this paradigm floating around with some fans that Superman music can only be good if it has an iconic, catchy, pop-culture-friendly theme to it. And there's nothing wrong if you insist on having that mindset, it's totally your right to do so.
But I'd recommend keeping your mind open, because Zimmer has a lot of awesome music for this new Superman...I'm just sayin!