I think a lot of people being harsh on Lukaku and ignoring some basic facts.
1. Is he dominating matches and putting the attack on his back? No he isn't but not many strikers are and Lukaku may still be a few years off of being able to do that, if he ever can get there.
2. He gets a lot of stick for being a 28 million pound striker. I would bet anything we aren't paying anything close to that amount.
3. This kind of goes back to point one but we knew going into this match what his weaknesses are. His first touch can be poor and his passing is nothing special. He is not going to beat people off the dribble with trickery. Only power and pace. Without Mirallas and Barkley we aren't a counter attacking team. Naismith can't run at people and he also has a very poor first touch so when he gets the ball played into him it almost goes careening 2 yards in front of whatever direction he is facing.
4. Without Barkley or Mirallas there is no one else for defenses to key on to and open space for Lukaku. His strength is power and being a very good finisher when on the break or open in the box. For a guy with his size his contested heading needs improving. If Barkley is gliding past midfielders and pushing the rush then the CBs have to leave lukaku and create more space. Now it will be Osman or Naismith pushing the attack in the middle and there is minimal threat with that.
5. So with him being our only big threat up top he is constantly doubled in the box. A lot of people see Naismith getting goals and E'too scoring and claiming they should be starting and Lukaku, but when you look at E'too's goal vs Krasnodor and Naismith against Chelsea not many people are pointing out how the space is opened up because two defenders are shading over and focusing on Lukaku. Even when he isn't playing well he still receives all of the focus and causes space for others.
Still Lukaku isn't playing well and there are some things that are frustrating and he needs to improve on, namely his runs which result in him being offside. Granted our midfielders aren't seeing them quickly but there are so many times where he is needlessly offsides and if he flattened his runs he could stay on and still have a head start on the defender.