Long story short, in my opinion, Halo 4 is the best Halo game so far.
(TL;DR Version: Halo 4 is the same, but different, and that's exactly what I was hoping for.)
Perhaps my feeling this way is because I didn't go in with any real expectations. If anything, I only expected it to play the same, but feel different. I was not expecting it to feel like I was playing a Bungie Halo.
Perhaps one of my biggest, and longest standing, hopes for Halo was one that grew after reading Fall of Reach and First Strike. That hope was that in future games, we'd get to see a more human side of John-117. And this is why I absolutely adore the ending of Halo 4. For 3 games, John-117 has been the embodiment of the perfect, invincible soldier. And for those 3 games, it was awesome! But I have always played Halo for the story, first and foremost, and I my initial excitement for Halo 4 was limited because I thought that it was going to be more of the same on that front. I didn't think the Master Chief would go through anything that would really test him, and so I was less excited to step back into his armor.
I am so happy that I was proven wrong.
Also, on another note, I don't want the Master Chief to die at the end of this new trilogy. At the same time, I also know that unless he changes and evolves into a more human character, he won't have a place in a more peaceful world, and so the writers would have to either kill him off, or pull another Halo 3 ending. So because I don't want either of those endings, I want the Chief to evolve and become a little more truly human. Since that is the direction Halo 4 seems to be steering him, I could not be happier with his continuing story.
I do miss Marty's music though.