I think there's a bit of a fundamental handling/physics issue with it - all it takes is slightly too much lean and the bike just oversteers helplessly into the trees. You can't always control it. Sometimes you crash and think 'what the hell happened there'. Maybe it's realistic, but for a game it's a bit much. The bikes are reasonably ok once you get the hang of them, but the sidecars seem borderline uncontrollable at the moment.
I love everything else about it, though. The TT course is beautifully realised. I still can't win a 'big bike' race though. I play on the higher difficulty levels because on the lower ones it's easy to win by a minute plus. On 'medium' and above, everything I do I still finish second, if I start from the front I'll be cruising round seemingly miles ahead of everybody then on the radar I'll see this little pink dot coming up behind me and the game's up. I can win on a Supersport, though.