Dont be so quick to write this game off.
The story is very immersive and keeps you hooked all the way to the end. The end however wasn't up to par with the rest of the story. It was a bit weak. The way the story is told, through a series of flashbacks, worked very well with the story and will keep you captivated completely.
The game itself is harder due to the new gameplay mechanics. You actually have a health bar in this halo game, which means you can't just run in and tank everything like you could as the Master Chief. Its not a bad element, its just very different and it actually works well with the game.
Personally, I feel that the second most people hear that the Master Chief isn't in this game, they immediately think it sucks. My advice is, give it a shot, it may not be as good as the other Halo games but that doesn't mean it's garbage. It's a solid, fun FPS that is worth playing.