I have a very simple reason for hating Concord and being slightly happy that it failed: They bait-and-switched the hell out of all of us with that reveal video.
You can't build up an interesting world filled with characters like that and then give us a PvP-only hero shooter. Who do you think you are, old Blizzard?
I didn't say they were interesting, we didn't get nearly enough interaction from them to know, but there was unarguably much more depth to them than "agent 123" in most shooters