Information from Gameinformer:
*** Potential Spoilers ahead ***
-Want it to be a jumping on point for new players without losing touch with what longtime fans cherish most.
-New hero called Connor/Ratohnhake:ton (pronounced Ra-doon-ha-gay-doo). He has an English father and Native American mother.
-More details about the protagonist/scenarios: You will experience Conner's childhood on the American frontier as he is raised by the Mohawk. The Mohawk eventually clash with white colonists who burn their village down, causing Connor to dedicate his life to confront tyranny and injustice.
-A new traversal approach that has players leaping and climbing trees and mountain cliffs.
-Uses a new version of the Anvil engine that can "depict thousands of troops engaged in bloody battle" along with highly detailed face close-ups. They later imply that if they used version numbers, they would be like going from Anvil 1.0 -> Anvil 2.0 or something of that nature.
-Judging by the images, the faces really are quite good.
-Combat is focused on putting you on the offensive and based on speed/momentum.
-The main character has thousands of new and unique animations (no carry over from other titles) to support the new combat system.
-Character details:
-George Washington: Interacting with Washington is one of the core relationships of the game.
-Benjamin Franklin: He's not a convenient inventor a la Da Vinci.
-Charles Lee: His role is a mystery.
-The game is set between the years 1753-1783 and is centered around the cities of Boston and New York.
-"It's not just going to a historical building now; it's going to a historical event."
-Event examples: "You will see the great fire of New York. You will visit Valley Forge as a location that is currently occupied by Washington's forces. You will visit these places in the moment that they were important, and hopefully, experience the reason why we know where they are today. That's the goal."
-Connor is in the heart of major battles, and they can now have a couple thousand guys on screen, whereas before it was capped at about 100.
-The overall story is still centered around the Assassins versus the Templars and Connor's journey.
-Not all the Colonists will be cast as good people, and not all the British will be cast as evil oppressors. They're trying to focus on how both the Assassins and Templars viewpoints exist in a gray morality as the Templars really believe they're saving the world.
-The French and Native Americans will also feature in the game, as was probably really obvious.
-The modern day stuff relates to that location in New York at the end of Revelations.
-There will be all sorts of wilderness in the game referred to as the Frontier.
-The map of the Frontier is 1.5 times bigger than the entire map of Brotherhood.
-The Frontier is not empty like in Assassin's Creed 1, but features a third of the game's missions and gameplay content.
-The Frontier also includes colonial settlements like Lexington and Concord and Connor's Mohawk village.
-You can hunt animals for resources, and how you kill them effects your reward. A one hit kill on a bear gets you a much more valuable pelt than stabbing it eight times.
-The wilderness traversal plays a big part in the gameplay in the Frontier, allowing you to use trees, cliffs, ledges, and more to set up kills and combat.
-Connor does have a hidden blade.
-The world changes as time passes, so a field where a battle happened in one year may just be a series of empty encampments a few months later.
-The entire world will change with seasons, so the cities and the wilderness will all exist in both Summer and Winter settings.
-In the winter, soldiers will move slowly and stumble about in the snow, and lakes and rivers will freeze over allowing you new terrain to work with. This gives Connor an extra advantage since he can still use the trees and wilderness pretty effectively during this time of year.
-There are all sorts of clubs and groups who want you to join and give you quests. These are separate from the mission system. These clubs will contact you based on what you do in the game. For example, hunting a lot will get you an invitation to the hunting society.
-There will be a goods based economy, a new property system, and more Desmond stuff.
-There's going to be some new puzzle thing like the first person Tetris.
-There's a new Animus database known as Animus 3.0.
-They're not unveiling anything about the multiplayer yet.
-There will be more platforming levels.
-Full synchronization returns, but with major tweaks. Missions have checkpoints, You also get significant rewards for doing these tasks instead of a 100%. "Imagine a leveling system in an RPG, except there's a finite amount of XP to find. The more in-sync you get, the more you fill your sync bar. Within each mission, each activity you complete has a value". You can replay everything to increase your score.
-They imply there is something resembling the Brotherhood system of picking up fellow assassins.
-Aligned groups are gone, but something new is replacing them in regards to factions. They don't say what.
-There's a new notoriety system that is more hidden and doesn't penalize you for exploring risky areas.
-The game has fast travel because the game has more traveling.
-Don't expect more tower defense.
-You can upgrade Connor's gear and costume as the game goes on in an attempt to make it feel more authentic.
-The cities have a lot more subtle detail now in terms of ambient things that happen.
-You can now leap over wagons or slide under obstacles, including navigating over and around moving objects. The free running stuff also has you jumping through windows to trees and then on top of church roofs. Basically, expect the free running stuff, but more fluid and presumably generally closer to the ground.
-Connor enters battle with two weapons. The game uses the same controls in and out of battle.
-The tomahawk and knife are a "constant presence" in battle. They also let you do double counters and multiple takedowns, and you can chain kills.
-There's no more target locking, it just automatically detects your target. Counter/defense are the same button to prevent turtling.
-You can use human shields and other context sensitive moves.
-They want you to constantly move in battle.
-There are lots of secondary attacks like the one shot pistol on the Y button.
-There's a new dynamic camera to track the action and make it look as cinematic as possible.
-There is a new sprinting system also, so you can hold the button to instantly turn around and start fleeing from combat. They also let you kill people while still moving so you can keep chasing a target. They kind of imply you can even leap off of them after you kill them, though I'm not sure if that makes you faster or just doesn't impede your movement.
-They really, really, really want you to constantly move. I mean like they say this every four sentences. Not just in battle, but in every section of the game.
-They also try to keep you more in control of the combat than ever before.
-Game Informer really loves their animation system.
-There are around 2.5 hours of character scenes in the game that are fully acted and recorded. They mean this in Naughty Dog style where they have the actors being mocaped while performing on a set that resembles the scene in the game.
-They're aiming for accuracy by having historical dialog consultants and actual Native American actors.
-This game has the longest development cycle since AC1, and has twice the production capacity (in terms of work hours) and budget of Revelations.
-They want the game to feel like AC3.5, and the game will have its first version complete in just a few more weeks, at which point they're going to spend the rest of their time refining it.
You think they should have it be the Finnish instead to spice things up a bit? 
