I've only seen the concept figures at Walmart. The local store sold through the first stock of it and I just saw more the other day, including concept Hawkeye.
Target and Walmart both sold through most of the first stocking of Avengers 3.75" toys and may have moved a few vehicles, specifically the Quinjet, but the 12" figures and most of the deluxe doesn't seem to be going anywhere. I think some of the role play stuff has sold also.
I don't know if it's going to be a bust or not or what Hasbro considers a sucess or failure, but for me, it'll be a failure if we never see Widow, movie Hawkeye, Fury or Loki's army at retail.