I did not enjoy the ship battles in AC3 but in this game they have been redesigned & you have full control of your Jackdaw. All the weapons are available with easy access from he mortar, fire barrels & heavy shot. Once you have damaged an enemy ship enough you get the option to board which then involves you killing a certain number of the enemy crew & other small tasks depending on the ship. The option to repair your Jackdaw after a boarding is an easy way to avoid your ship getting destroyed when taking on a fleet.
There are so many side quests in the game from Assassin contracts, Mayan puzzles, Treasure Maps, Underwater wrecks, Kenway's Fleet mini game & much much more that you can very easily get distracted from the main quest. I managed to complete most of these with only a few shipwrecks left to explore, on the world map you can also collect animus fragments & chests but these don't really reward you much in the game & I had begin to tire of the 'gotta collect them all' gameplay.
Playing the game on the PS4 with all it's hardware prowess really made the experience that much more enjoyable & the share ability allowed me to take screenshots & create videos with ease.
The Ubisoft formula (main quest will added pointless filler collectibles) being applied to almost all of their releases like the AC, Far Cry & upcoming Watch_Dogs is getting very predictable but where do excel is in the main quest & relevant storyline which is why I expect that next Christmas I will be playing the next assassin creed game in the series.