In terms of people actively ****ing, not too long. Couple more months. In terms of people remembering? Longer, much longer. As someone else said, whenever ME comes up, it's the ending that will be discussed.
I like the game, I liked the ending till the ending (ie. I liked everything up to meeting a certain glowing person). But the basic continuity issues drive me up the wall. Forget wanting a happy ending, I want an ending that doesn't violate continuity.
The problem right now is that I don't trust Bioware to make great games. Just decent ones. I won't say I'll never buy a Bioware game again, I will. But I won't be pre-ordering CE's anymore, That means less money for EA.
As for ME3, I won't buy ANY DLC until they do something about the ending. I'd even be satisfied with a patch that fixes a certain scene with the Normandy to make sense.
I'm a core customer, I've been a bioware fanboy since BG1. Bioware was the only company where I would always buy any game they make that was available on my platform (PC right now.)
Many other people feel the same way.
The psychological lit supports this, by the way. People can enjoy an entire book/movie/TV series and if the ending disappoints, they'll remember the entire thing badly.
There wouldn't be half the hate if the ending made sense, y'know. It'd be kind of lousy, but the continuity errors are just so glaring.