When he faces the goal = good. Channel running, powerful dribbling driving towards goal, good cross to Lingard and pressuring of defenders.
With his back to goal = bad. Doesn't win headers/position, awful first touch and lumbering around when not involved in play.
Surprised Mourinho doesn't call him up on this. One simple ball to your striker, some hold up play means your whole team can push forward and pressure the opposition. With Lukaku you don't know what you're gonna get in those situations.
Can't fault his mentality, just needs more guidance from his coach.