I've seen some people talk about Ravenous as the second game in the MercurySteam trilogy, but I believe that MercurySteam always wanted to follow on from Fusion to complete the story being told there(which is supported by the fact that they actually pitched a Metroid Fusion remake originally, and then their Metroid 2 remake heavily connected it back to Fusion).
1-3 is the "Hunter", "Orange Suit" or "Metroid" trilogy.
4-6 is the "Hunted" or "Blue Suit" or (possibly) "X Parasite" trilogy.
In the first trilogy, Samus is the hunter. Her mission is to seek out and destroy Metroids and Space Pirates. She has her classic orange suit throughout, and it ends with the eradication of all Metroids, and the destruction of Zebes, where it all began. It tells a complete story.
In the second trilogy, Samus is on the back foot thanks to the X parasite. Her suit is nearly destroyed, it is now blue, and it is regrowing over the course of the trilogy.
The Metroid DNA saves her life, and it starts to change her. She's also being hunted by the SA-X, then the Emmi/Raven Beak, and now the Space Ninjas/remaining Mawkin Chozo.
I think Ravenous will see Samus reach her full potential, fully restoring her suit, and I cannot waaaaait.