(1) On Mars, Shepard will be looking for a Prothean secret weapon which may be useful against the Reapers. Casey Hudson is quoted with saying that this doesn't mean the story is about THE McGuffin what will win the war, but more about "searching the whole galaxy for pieces of useful knowledge and war assets".
(2) At the start, people on the Citadel will believe that the war isn't their problem. This will drastically change in the course of the story.
(3) War assets can be all kinds of things from fleets to single people. Their contribution will of course be of drastically different sizes.
(4) If you enter Reaper-controlled territory, there's a chance the Reapers will try to hunt you down and you must do something to avoid them. That's referred to as a minigame.
(5) Reaper-controlled territory will change as the story progresses, but only main plot decisions trigger these changes. You'll have all the time you need for sidequests.
(6) Some missions are mutually exclusive. Which one you choose from a set of options might affect the fate of civilizations and the loyalty of NPCs.
(7) Some optional missions may become unavailable if you don't finish them before certain story events happen. That might adversely affect your campaign.
(8) Re-found snippet. There will be a krogan on board the Normandy. (I had removed this entry because I couldn't find the quote anymore, but Casey Hudson was indeed quoted as saying this, as an example of that there will always be an NPC around personally affected by Shepard's story decisions. In the same sentence, he also said there will be a quarian on board, but that's hardly news, LOL. Note that this does not necessarily mean that any of those "characters from everywhere" (CH) will be a member of Shepard's team.
(9) All missions may influence your reputation with NPCs (unclear whether this only refers to team members). That in turn may influence your interaction with them in future. NPCs differ in what they prefer, some may be more impressed by Renegade decisions, some more by Paragon decisions, but all will be influenced by decisions affecting their species.
(10) If old team members are dead, different things may happen depending on the character. Sometimes a story arc will be completely lost, sometimes there will be a replacement character, sometimes the story will develop in a totally different way.
(11) There will be no "Reapers win" scenario, based on the reasoning that such an ending is unsatisfying for players and would lead to re-loading a saved game anyway. There will, however, be endings where whole species become extinct and many worlds are destroyed, including Earth.
(12) The Collector base decision will become important at some point, but whatever you did with it will not have any negative repercussions (How they'll manage that and make it still be important I'm curious to see).
Update - translated quote from the article "At the end of the game, everything can happen. Then even the big decision you had to make at the end of Mass Effect 2 will have an effect." The follow-up that it will have a big and meaninful consequence appears to be more speculation by the writer of the article than real information.
(13) How the war progresses will also affect the Normandy somehow.
(14) The Citadel will be bigger than ever before and you'll meet many characters you know from the first two games. Many loose ends from the first games will be tied up, including the mystery of the Keepers. (I hope I'll meet Chorban again).
(15) Casey Hudson is quoted as saying that it is "a good idea to stick to your principles" with regard to your style of action, i.e. Paragon/Renegade. And I hoped we wouldn't be railroaded onto one path this time.... Though the context suggests that this might be NPC-specific, i.e. you should stick to your principles with regard to decisions affecting one character or species. I would like some clarification on this.
(16) Liara will join Shepard's team on Mars.
(17) Shepard will not command fleets or move around armies.
(18) EVERYTHING Shepard does will affect the war. Story missions, sidequests and even exploration minigames.
(19) There will be a menu listing everyone's contributions to the war assets. Casey Hudson: "For example, there may be an entry for the quarian fleet, which is worth a crazy amount of points, and an entry for a single guy you've met in a bar and convinced to join the army, who is possibly worth a single point."
Edited by Ieldra2, 22 January 2012 - 10:06 AM.