1. If you get close enough to a person, e.g. following Yusuf at the beginning of the game, Ezio will go into autopilot and walk with him.
2. All memories concerning the Keys in Constantinople will be accessed through Sofia. The Altair memories within the Keys will be relatively short, but engaging. You do not have to activate the Key as soon as you touch it, leading to possible replay-ability of Altair memories as well.
3. There is an achievement/trophy for reaching the top of Hagia Sophia in under 30 seconds.
4. You can take a break from playing Ezio and return to Animus Island with Desmond through the menu. Doing so, Desmond can talk to Subject 16 and even hear the voices of Bill, Shaun, and Rebecca from the outside world. It is noted that Bill trained both Desmond and Lucy at a very young age.
5. Ezio can control his speed whilst zip-lining. (the faster option will attract a guard's attention)
6. You can test out bombs while crafting them to see their effect.
7. The 'random quests' can be anything, including moving 5 boxes across a street.
8. While disguised as a minstrel, the face buttons (X,B,Y,A on Xbox) has Ezio use different songs, mostly about Cesare. Pressing the right control stick activates Eagle Sense.
9. Ezio will aquire the Armor of Ishak Pasha, the Revelations counterpart of the Armors of Altair and Brutus.
10. Ottoman guards are marked on the mini-map with a yellow dot.
11. Ezio will fill the new HQ with books in place of paintings.
12. Ezio has all his old gear (including parachutes and the crossbow) from the beginning. Tunnel Booths have also returned.
13. Assassin recruiting will be more diverse than just saving civilians from guards. Some can be done through quests, e.g. catching a counterfeit thief or winning a race. The new Recruits will be categorized, involving the weapon they are most skilled in. In order to reach the level of Assassin and Master Assassin, your Recruit and you will have to track down a Templar Agent.
14. There are Animus Data Fragments throughout the city for Ezio to collect. These appear to look similar to the AC2 loading symbol.
15. The second Key is under Galata Tower. The only video we have is of Ezio almost falling to his doom.
16. The second Altair memory will take place directly after Al Mualim's death, leading to a fight with Abbas's followers and climbing to reach Abbas to retrieve the Apple. (Be careful of the Apple's pulses while climbing)
17. The third Key is housed in the Forum of Ox. In order to get there, Ezio must use Eagle Sense while perched on a view point to pick up hidden symbols leading him there. The Forum of Ox features a chase with Templars in a boat as riflemen shoot at Ezio.
18. The third Altair memory takes place after Altair's son, Sef, is killed. Not much is known other than Altair having to fight fellow Assassins to escape Masyaf.
19. There will be at least 9 Multiplayer characters in the Campaign. So far the confirmed Templar Agents are the Crusader, Renegade, and Trickster, Deacon, and possibly the Thespian.
20. There will be 5 new maps (Galata, Antioch, Knights Hospital, Souk, and Ippokratous) as well as 4 returning maps from Brotherhood. (Mont St. Michel, Rome, Castel Gandolfo, and Venice) "Training Ground" as seen in the Beta is now confirmed to be a 'noncompetitive, untimed mode' allowing you to 'explore the map, practice your abilities, and kill assigned target VIP' NPCs.
21. Uplay has just released the requirements for Revelations, Rearmed, and Recollection. If you try to go into the official Actions and Rewards page, you won't find it. http://uplay.us.ubi.com/