It’s only 5$ for the people who don’t get it for free witch is still a good deal for a whole campaign. 
Is it automatically free if you have the Master Chief Edition?
You need the Master Chief Edition to play it at least
Yes if you played it before December 19th, you should’ve gotten a message from Xbox, inside you’ll find your code 
How does it look?
It looks good
Fantastic! The cutscenes look amazing in 60 FPS, and the gameplay is smooth. 343i did a good job on it.