He did a job in his first season. The hate is because of his disgraceful second season. I've said it before and I'll say it again - for the first half of that season I firmly believe he was the worst regular starter in the entire league. All the while he was quite obviously blaming our other players and talking about himself being 'a big man' or whatever rubbish he was spouting at the time because he was a teachers pet. He got a bit better once Ole came in and dropped him for a while, but then proceeded to shit-talk us and make training information public once he left.
There are very few ex-players that I like to see fail after they left. Basically just Tevez, Heinze and Di Maria. Lukaku is very close to the same level for me.
Edit: I just realised I must really hate Argentinian players.