I really hope they actually use ME4 as a opportunity to tell the rumoured story about the "dark energy creatures" that eat suns. That subplot in ME2 was so intriguing, but seeing ME3 devolve into a rather simplistic and cliche route was unfortunate. I really wanted to see it become about the Reapers taking the extreme measures they did because it was the only thing holding back a far more sinister evil.
Red for me. 
And imho, it will be interesting to finally see the dark energy plot. Because there were so many hints in ME1 & ME2 and we are led to believe that some sinister event is about to happen and then in ME3...
Oh, sorry, we forgot about dark energy, this never happened pls. But the lead writer of ME1/2 left and I guess they didn't want to go into that direction. Plus, from what I've read in his interviews, the idea was really underdeveloped.
I thought that they were running with that 'dark energy' ending, and then it got leaked, in its entirety, in November 2011, months away from release. The writers had to lock themselves in a room and rewrite the entire ending in very little time, hence what we ended up with. I don't remember any issues about the team changing the story because writers from ME1 and 2 left. I was under the impression it was all due to that infamous leak.
But it wasn't tainted, at least according to Cory in DA2. He made it clear that the City was already Black when he got there, and the whole Golden City was religious propaganda. Not far from your "humans muck things up" take on it, though... Just a different group of them lol.
Corypheus being clear on his opinion unfortunately doesn't make it clear canon. For all we know, his presence caused and created the taint, as the chantry suggests, and his first observation of the Golden City was it already tainted by himself and the other magisters. Having said that, it's certainly possible that his reasoning is true as well - as has already been said, we'll just have to wait and see what Bioware do with it. I just don't think that Corypheus' words bear a dreadful amount of weight, on the topic of the Golden City.
As for ME4, well... my enthusiasm for ME has been killed, resurrected and then killed again a few times. I'm just done with it. Obviously I'll wait for reviews before thinking about getting it, but even then, I'm worried that the first game might be good, the second game might be great, but the third game will disregard its series within 10 minutes of the end (assuming new trilogy). I don't want to have to wait 5-7 years to decide to get it or not, but I'm kind of stuck unless they confirm it's stand-alone.
Haha, that's a very interesting point of view. Personally, I can still play Mass Effect 1, 2 and 3, and enjoy most of it, despite not particularly admiring the endings in 3. Even if they screw everything up at the end of the third installment of the new Mass Effect series (if it is indeed a trilogy), if the first installment is really good, it wouldn't change the fact that the first installment is really good.
For me, you could compare that to anything. A failed sequel doesn't tarnish what's already made, even if it's directly part of the same story. I quite enjoyed the first two Hobbit movies, though I wasn't particularly impressed by the Battle of Five Armies - doesn't mean I enjoy the first two any less. Aliens was great, Aliens 3 less so - doesn't make Aliens any worse.
Having said that, I can understand how others might have different opinions, but this is my own.
And IRC there are going to be 5 DLCs for MP. We already got Destruction and now Dragonslayer.
5 MP DLCs? Really? Where did you hear that? That would be awesome if it's true 