I wasn't as critical of Mayo as probably 95% of Patriots fans were as he took over a team that had the #3 overall pick and a weak roster.
However, the team kept making the same pre-snap mistakes with penalties and there were some clock management issues. Then you have some of the comments he made after the games that didn't sit well with the players and fans.
I do think firing Mayo was made easier by having the chance to bring in another former Patriots player in Mike Vrabal who has coaching experience. Not sure who they bring in, but I'd lean towards him as of now.