It depends on what the job is.
Is it to safely keep Everton upper mid-table? Then yes, he's the man.
Is it to get us closer to, or even ahead of, the six clubs that are currently better than us? No, barring a sustained run of luck.
We're paying him all of that money, and spending tons on the types of players he wants, for the modern Premier League equivalent of Moyes results. It's a huge waste. We could get a lot more for the amount of money we're willing to spend.
Edit: In retrospect, it's a slightly disturbing that unattached Lucien Favre was on our shortlist but we chose to pay a ton for Koeman instead. We spent more for a manager with an inferior track record. The board needs to stop worrying about this "proven in England" nonsense. The majority of the top-end PL managers, and even players, that we've seen in recent years have come from outside of England. You get less for more when you shop in the Premier League.