Well, I think that the Chicken Littles are mostly the same people that were panicking over first quarter completions surrendered when the team was en route to 17-0, so I tend to laugh as I read their posts. However, the switch to the 4-3 was supposedly done because of Mayo's potential, and it's not working out. Part of the problem has been the stupidity of trading Seymour, part of the problem has been Mayo's injury, part of the problem is relatively poor play by the other linebackers.
However, when you look at it overall, there's no question that, to date, the move to the 4-3 has failed to turn Mayo into the player New England thought he would be with the system change.* I expect that time passing for the injury and the gaining of experience will help, but I also think the team needs to replace the other linebackers in the corps and either get back to the 3-4 or trade Wilfork and Warren for other D-linemen, because the 4-3 is limiting their impact.
*Disclaimer: I wanted Clady with that pick, so assign whatever bias you feel is appropriate.