All right, here's my thoughts on the subject:
It's true that Halo did up the standards of console FPS to a certain degree. And it's not a bad series, just not as good as it sounds.
Now, I am a long time fan of Bungie and a huge fan of the Marathon Trilogy and Myth. Now, when I was awaiting the first Halo, I expected to basically see Marathon again. I started getting hopeful when they again paired the main character with an AI partner, but I was disappointed by the lack of depth that made me love Marathon.
I'm gonna pause and say that I found Master Chief's voice completely annoying. If a character is going to speak, he should at least have SOME fucking emotion.
Anyway, I was rather disappointed that Halo one didn't live up to my expectations of being the next Marathon, but that was fine because I enjoyed it. Now, Halo 2 came and I again hoped to see some reference to Marathon. Once more I was disappointed. The same can be said for Halo 3. In the end, it just seemed like Bungie just made the same game three times and only added and modified a few things.
However, I at least expected Halo to have a story depth resembling Marathon. Again, my hopes were smashed upon rocks. However, they did do what they did with the end of Marathon. That is to say, not have a REAL end. Anyway, I'm going to bash or praise Halo. It's good for what it is, but could be better (start with better acting. I only liked Halo 2's cast because Ron Pearlman plays Lord Hood).
Anyway, that's all I have to say. So feel free to burn me at the stake, crucify me, or whatever it is you hardcore Halo fans do when something like this pops up.