SHIELD has been okay. I imagine they didn't want to go all in and then get cancelled. The show is a slow burn. They've been expanding the character's backgrounds and working on the interpersonal interactions.
Now they know they have two seasons they might invest more in the story.
Angel took a couple years to really get good. The first season of Buffy was shaky. And I wasn't sold on Dollhouse until I saw the first season finale set in the future.
I think Angel was good the first season and a half and then after Connor got introduced it got crappy, but I hear what you are saying. The problem is even with steady improvement I'm not sure people who watched and left are going to come back.