All Lukaku needs is a bit of consistency and focus. He's been great on loan at Everton this season, and I'd happily take him in the summer if we've got the money and Chelsea are willing to sell, but there's been times where he's looked incredibly average.
I'm not really complaining though, he's scored 15 goals for us and helped us to 5th place. If Mourinho keeps him around and puts him to work, I could see him becoming one of Chelsea's most important players in a couple of seasons.