Here's some gameplay footage of Assassin's Creed: Rogue..
Check out who makes an appearance at 00:45
Based on the commentary, the Morrigan ship will be faster and more maneuverable than the Jackdaw in AC IV.
The Morrigan also looks to be more well equipped than the Jackdaw was. The Burning Oil will be pretty awesome to use. (Multiplayer Naval Battles would have been awesome!)
We also see the same seamless transition from Naval to Land like in AC IV.
The whispers that Shay hears when there's an Assassin close-by, is very similar to the Multiplayer modes in previous games. Again, some features that Ubisoft has used their Online Multiplayer to test out before incorporating into the games.
The Assassins look like a tough challenge but the Templars also look very well-equipped to give Shay the advantage.
Now for some more Naval Gameplay..
Again we see our favourite Templar, Haytham Kenway.
The Morrigan looks really powerful with it's many different weapon options. Looks like it will be a lot of fun!