Shamrock Rovers and Baggies fan here so probably qualified to give an opinion on Michael O'Neill. Won back-to-back titles and brought Rovers to the Europa League group stages - first Irish club to do it and it's an amazing achievement.
Equally with Northern Ireland, became the first (and only) bottom seeds to to win a Euros qualifying group, again an amazing achievement.
He's a very impressive bloke and a top manager IMO, only caveat is that his best work has been done as an underdog where tactical nous has beaten better sides. Don't know how he'd get on with one of the favourites in the Championship.