He was in charge of the absolute best gaming series of the last generation of gaming, the absolute best game of that era (Mass Effect 2) which is also my 2nd favorite game of all freaking time, which I still replay through once every 3-4 months (this year alone I've beaten ME2 4 times. I don't even do trilogy runs that much, just take my ME1 Lv60 save with all my favorite decisions and play through ME2). ME2 pretty much saved me during the worst year of my life, so that means Casey is responsible for saving the worst year of my life.
That being said I still have hope for ME4. A fresh perspective could do wonders for the next game. I think Casey wants us to feel more positive about the future of ME with his departure, not more negative. But we all know what people on the internet are like. It's a cesspool of miserable people with crappy priorities, morals... pretty much anything that makes a decent person. Casey will be much healthier mentally when he doesn't have to hear crap about ME3, a great game in its own right, when all he wants to do is make a new IP.