I'd be lying if I told you that I'm more than a little bit concerned after reading through this editorial on PC Gamer that spells out how Mass Effect 3's single player ending is impacted by the number of War Assets you have or have not accumulated in the game's multiplayer mode. Am I the only one learning that they've added a pay-to-win marketplace to the multiplayer component for the first time?
I did every proper quest I could find in Mass Effect 3, made sensible decisions that didn't conflict with my choices in the previous games, and brought people together. But I still got a gallingly bleak ending.
That's because I'd never played the multiplayer. It's a co-op mode where you and up to three other players have to survive waves of AI enemies and complete objectives. If you succeed, you get an increase to your Readiness rating a percentage by which your single player War Assets are multiplied by. These are specific to each sector of the galaxy, so if you have a lot of War Assets in the Terminus Systems, you'll gain more by playing on a multiplayer map set in the Terminus Systems.
It's all rather. dirty. Presumably they're trying to encourage you to try the multiplayer because to do well in it, you have to buy or earn unlockable items, and you can get these for real money. But they're doing it by hurting your single player game, slapping a good playthrough with a bad ending as a penalty for not playing co-op. Even if you like co-op, it's not unreasonable to want to play through the single player first.
It is possible to get the best ending in single player without playing multiplayer, but it's twice as hard. All your War Assets only count for 50% of their potential value. The biggest gains in War Assets come from a culmination of your decisions in the previous games and your decisions in this one: if you've helped a race before, and you help them here, it's often possible to get their full support and resolve their conflict to get someone else on your side too.
In other situations, a wrong call somewhere along the line, or a Paragon or Renegade score too low to pick the right thing to say, can mean a character dies, a race is demoralised, and if they fight for you at all they're worth much less to the war effort.