343 have done a great job in revitalising the Halo franchise.
The sound has been beefed up, the graphics are gorgeous and the story line ties in nicely and captures you. The multi-player remains fast paced, vast and customisable. The new addition of "Spec Ops" to provide an alternative perspective in an episodic format is a great idea and give the play an alternative to simply repeating the main story missions.
The legendary difficulty is at a nice level, tough and requires patience (especially if you are playing solo).
Great game and a lot of fun as always, though this is the 4th in the series with the addition of a new enemy species it could also be suitable as your first introduction to the Halo franchise.