Lukaku is doing brilliantly for us at the moment and a lot has been said about Mourinho loaning him out. From what I have seen of him so far, he is another one who is quite inconsistent and I can see why he was loaned out. When he first come he would be brilliant for 35 mins, tailed off and then looked exhausted after 60 mins. His fitness is improving as he's playing a lot of 90mins, however there is a lot for him to learn before he becomes a top class forward. He has a knack for getting in the right spot which is what you want from a forward but his first touch and awareness need to improve a lot. He also needs to be more involved as he tends to drift in and out of games.
I would say he's not at a level where Chelsea can say he's the no1 forward and trust him to start every game, he would be under a lot more pressure there and the way teams set up against Chelsea would mean he would be isolated upfront on his own and would need to hold the ball up much better than he does now. As for the links to Barcelona, there is no way he is anywhere near technically good enough to play for you and probably never will be as that's another step up again from Chelsea.