I'm on the fence with this one (and Black Ops 2, for that matter). My sole experience with the Halo franchise was a borrowed copy of Halo Reach from a Co-worker, and to say I didn't like the game is an understatement. All I remember about it is 3-4 hours of utter boredom.
Halo 4, though, looks interesting, and footage of it reminds me a lot of Metroid Prime, which appeals to me so much more. I'm especially interested in the apparent new focus on storytelling, something I thought was severely lacking with what I played of Reach. That said, this is the 5th game (7 if you count ODST and Halo Wars) in a very long-running franchise at this point, and no review I've seen has made it clear whether this can be a jumping-on point for newcomers. I'm also not an XBox LIVE Gold Member and I never will be, so the multiplayer is probably completely worthless to me, so I don't know if the campaign alone will be able to justify that $60 with so many things I'm not certain about with this game.