You really need to read en Everton fan's view.
@BigDunc9 clearly said that many teams have set up to close shop when playing against Everton and Lukaku has been able to break through these teams. But let's leave that for a minute.
Last season we had Zlatan with us along with the likes of Pogba, Mkhitariyan, Mata, Martial, Herrera - all of whom are technically gifted in their own rights. Yet we were unable to convert our chances or break teams down. You would think that we should have scored far more with that line up of players but we were atrocious. So to assume that one technically good player will suddenly improve us is a massive leap of faith.
What we need is better play from the team, better transition which will help us to move the ball quickly. Lukaku is quicker than Zlatan so that is one thing in our favor that he can actually act as the forward playing off the shoulders of the last defender. That will help us in getting behind tight defenses too. Moreover, no one here says Lukaku will suddenly turn us into world beaters. Doubt even Messi would be able to do that for us. However, as a young striker yet to reach his prime and who has shown consistently that he can be a 20 goal a season striker in the PL, it is well worth the risk. The only other striker I would have from a rival (as an out and out #9) would be Harry Kane. But we all know that it is nigh on impossible to prize him away from Spurs especially at this stage. Even then the cost would be easily 100 mil pounds plus for Levy to even think about that possibility.
Think Mbappe, a guy with half a good season under him and being touted as a 100 mil plus player and we are getting an established PL striker (who is only 24) at 75 mil. I would say this is a very good deal for both sides. Lukaku would really help us in Zlatan's absence. He won't make us champions all alone because we will need far more than that to get over the line in terms of goals from the remaining side. However, he will help us go a long way in the right direction.