Here is my honest opnion. It's good music. It's the type of stuff you could watch buildings and cars go kaboom to.
However, it isn't great to us because it is no longer the music we are familiar with.
Whether or not you like the new music more, the old music had a common way of going back to the monk-chanting sounds of the first game's title screen theme. Even Halo Wars had bits and pieces of the theme in it. A good example is "Spirit of Fire," which makes a slight, yet effective, use of pieces of the theme.
The theme of what we called "Halo" is gone from Halo 4. The closest bits are the parts of the title screen music in the new game that feature the "Cortana" song.
By the way. Did anyone else find it extremely awkard when, in mid-battle, the music would cut off? It made little sense.
(P.S. I am a fan of Halo 4's title theme, but overall, the game's music was...good...not great)