Depends what you mean as stellar. Royle worked miracles at Oldham (like Martinez at Wigan), maybe more so than Martinez. He got Oldham to a League Cup Final and 2 FA Cup Semi Finals. He got them promoted to the top flight for the first time in 68 years and kept them there for 3 seasons. He saved Everton from relegation when we were absolutely dead and buried - I lived through that era and remember it vividly, the miracle that Royle worked in revitalising the same bunch of players was incredible. He won us the FA Cup, beating 3 top teams along the way - 6th placed Newcastle, 7th placed Spurs and 2nd placed Man Utd, so not exactly an easy feat. The next season, buoyed by the inspired signing of Kanchelskis, our 6th place finish was the highest in 6 years. Royle's record was very good. The following season we had a dip, which we may have rode out if Johnson hadn't been such a massive dick and sacked him. Moyes had a dip in his 2nd season too, we stuck by him and look what happened. Royle then took Man City from League 1 to the Premier League in 2 successive seasons promotions. He also took Ipswich into the Championship play offs in 2004 and 2005.
I'd say Royle had a pretty good managerial career.