The difficulty curve in this game is pretty awesome imo. Since I had some experience with Top Spin 3 I startet my career with the Hard difficulty setting, but as I found out it was too easy for me, so I startet again on Very Hard. Lost the first Minor in the finals, then won all of the following Minors. Exactly the same thing happened with the Majors.
But then came the Masters - In my first 5 tournaments my best result was semifinals, I always got crushed by Nadal and Djokovic. In my sixth Masters I faced Nadal again in the semifinals and lost the first set 3-0 (I'm playing Top Spin length). Thinking I'll get crushed again for sure, I started to experiment a bit, tried different things - and I actually won the second set 3-0! And then I won the following Super-Tiebreak 10-7. It was an amazing feeling.
I haven't lost a Masters since then, but now I'm struggling with the Grand Slams and Special Tournaments. Got crushed again, first by Nadal in the Continental Cup semifinals, then by Davydenko in the Roland Garros semifinals. But I'm sure I can manage this as well.