As someone who played the previous games, I'm the first to admit the series was getting stale, and 3 looked like it would help fix this problem. And indeed, the story I thought was the best one so far, but that I feel is the only thing the game improved upon. Elsewhere, it suffered.
For one, fast travel is now a lot worse. Finding tunnels is tedious. Horseback is pointless because they refuse to go down hills, of which the Frontier mainly is. This is one of the biggest problems. The Frontier is needless. I understand it's the setting of missions, but these could have existed outside the travelable zone. Otherwise there's little to do besides collectibles, travel is a pain, and hunting? You can literally run around with your blades out.
There is a greater variety in missions, but 100% on some of them are the hardest missions in any AC game so far. And while we're on missions, we need to talk about characters. I'll list the likable characters: Paul Revere, the Mohawk shaman, the Homestead recruits, and the Assassin recruits. Connor is the least likable protagonist so far. Altair was arrogant but trying to redeem himself, and Ezio was smooth as hell and a master assassin. Connor is selfish, out for revenge, and doesn't seem to care about helping a huge cause, only motivated by his own desire, and in the end this leaves him flat. Many of your allies are douches as well, and while the duality of both sides having good points is interesting, it ultimately leaves the player dissatisfied that they aren't a 'hero'. Also, Connor's story just kind of... ends, and the epilogue missions are just cutscenes.
There are some positives though. Naval missions are FANTASTIC, the best part of the game, there was clearly a lot of time put into it. The Homestead is a very cool idea, and the missions for your friends do make you feel good. We do get to play as Desmond, but only in a few missions, and they're incredibly easy. Multiplayer is still fun, and the new mode Wolfpack is excellent.
However, with all that, the thing that brings the game down is the glitches. So many things left unfixed half a year later. Recruits not being marked as complete, leaving 100% missable. Clothes and items changing randomly, characters not appearing, ammo vanishing, optional objectives becoming failed after a success, and many more. They take the game and just delete the fun.