lukaku's an extremely limited footballer. he is useless outside of the box.
Pretty much this, he's a rough "diamond", give him a few more years to become a proper football player. Doesn't help that his amazing physical attributes (for his age) aren't as good in the EPL where the game is overly physical and fast.
In Belgium where defenders are much weaker and slower, Lukaku could easily hold them off and shove them around. He couldn't dribble, shoot from mid range nor pass though, he mostly scored tap ins thanks to his big bulky body. But he's just 18, he might come good, give him a few seasons. Apparently he wants to go back on loan next season to Anderlecht and the club is preparing an offer.