I just got done playing the latest episode. Don't worry, no spoilers here but I'll have you know you're in for a good experience.
Completely new environments, scenarios, objectives, music, and even a new enemy type. I even think the Promethean Knights got an upgrade also. They kept doing their MW2 Commando lunge, but a good thruster pack stops that. The new maps include a lot of parts so that they'll stay fresh through multiple play throughs, and they look a lot better than the original SPOPs maps as well. The lighting is gorgeous on them, and only ONCE did they overdo lens flare! Crazy right? We all know how 343i loves lens flare.
The download for the later 5 chapters is 2.21 GB, so unless you got a good download speed you'll be waiting for a while sadly.
I give Chapter 6 an 8/10.
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I felt that Chapter 6 of SpOps was fair better than episodes 1 - 5.