For me too. It's definitely not strictly better than TS4, but once you get the feel it's quite good.
As for the AI changing: I get the feeling they give you an opening more in the later sets. But I've had the opposite happen. They should make an attribute for it, some sort of morale stat.
Could it be that the court feel is incredibly different? I was being decent on hardcourt but on clay I just lost against a crappy player with worse stats. In TS4 I never really noticed any court differerence.