O'Neill said: "James came in here for a big fee but he was not affected - not at all. He knew the scene before he came to Villa from his loan season although the revamped training ground would have been new to him."
He added: "He settled in very quickly and I am sure James would be the first one to say 'you paid it, not me'. But to me anyway he justified the fee.
"Players can crumble under transfer fees in certain cases. It is alright a player saying 'someone else paid it' but you have been given a valuation and for a while you have to cope with that.
"It can a bit uncomfortable for a few weeks until you get used to it but James was first class."
O'Neill added: "The reason James wasn't in the side to begin with was because we had kind of settled down for a bit but I always knew he was going to be a major part of things for us and so it proved.
"He was expected to get up the pitch, support and create and score the occasional goal but the work he did defensively, getting back and covering, was also terrific.
"Having played that position, I know how difficult it is. It is really physically very demanding but James has got a big heart and he will improve again."