I would consider The New Order a great game just for its very polished combat sequences, but its well told alternative history story and the way it's integrated with the gameplay make it an even rounder experience, aided by a very atmospheric world design, with some beautiful and fun to explore environments that invite you to take some time just to look at them. Although the enemy AI is nothing special, the firefights are very satisfying and, something that positively surprised me, being stealthy is many times a viable and entertaining option.
The Old Blood is a more action-focused stand-alone expansion with a simpler story that is clearly a throwback to older Wolfenstein games.
Shorter than The New Order but full of thrilling shooting moments, I had a lot of fun playing it, but probably not as much as with the main game.
More info: https://en.wikipedia.org/wiki/Wolfenstein:_The_New_Order
More info: https://en.wikipedia.org/wiki/Wolfenstein:_The_Old_Blood