Massive naval navigation and tropical islands start to get repetitive in about the 6th sequence of the campaign. Edward Kenway is way powerful enough and hardly a moment in the game when melee combat offers challenge. Even when you are outnumbered you can just use a smoke bomb and clear out the groups. The best part of the game is the naval warfare and its really tough in the first few missions when you have to take out ships as yours isn't upgraded. But once you get the hang of it and upgrade your ship using the required materials you can breeze through the game easily.
Black Flag does have a long campaign but it gets repetitive and can bore easily. The eavesdropping missions are a big big nuisance and so is the tailing someone. These types of missions are so overused by Assassins Creed. This time they went for a huge game and a big map and so much stuff to collect. At one point I just gave up and went through the missions straightaway and realized how drab and boring they were and offers nothing new. You have a 100 islands now and all of them have towers to climb and chests to loot and animus fragments to collect. There is also the shanties which are musical lyrics spoken by your ship's crew. Then you also have many a underwater shipwrecks to go down and collect more animus fragments and chests. After that you have the treasure maps which was the only great thing in terms of all these collection assault by Ubisoft. Its cool to look at a treasure map and then match it with the actual place and gives great satisfaction.
Far Cry also uses radio towers and so does Assassins Creed. Then you have the skin animals thing and make pouches and stuff which is also there with both the games. You have chests to loot in both the games. The AI is easy in both of them. The point I am making here is that Ubisoft needs to now come up with something new and better than the same old and overused formulas. Also having thousands of stuff to collect is not a great way to increase game play hours. The campaign even though long is very repetitive, especially the missions on sea and those with tailing someone and eaves dropping.
The only plus side of the game were the Templar missions which reward you with extra armored clothing and some of the naval battles.
The first 12 hours of the game are enjoyable as I sifted through the ocean and scouted for ships to plunder and upgrade the Jackdaw (Edward Kenway's ship). I traversed through entire Havana, Nassau and Kingston and completed all achievements including assassin missions, towers, looted chests, collected animus fragments and shanties. However I realized that these are spread all over the huge Caribbean map and have no end. Practically the makers of the game thought lets throw in thousands of things to collect and that will make the game long. I was really excited as to how the game started out and by the time it was halfway I just wanted to go though the missions for the heck of it. Naval warfare repetitive, melee combat and mission approach repetitive, islands and the look and feel of the areas repetitive and typical boring AI that never offers a challenge.
You add this all and you got yourself a 100 hour game that should be finished in 12 hours and avoid all the unnecessary extras. Ubisoft you cannot make a great game by giving 100 towers to climb and 5000 things to collect. Stop mixing AC and Far Cry to the point where players feel ripped off. The story is average and the game feels more like a process than fun.