Depends on how you look at it. I've been playing for about 2 days and I'm just over 50% in. The real fun I think will come after you have acquired all the bikes you want and can then race just for fun. I hate to say it like that but the AI is just horrible. Sometimes it may seem like it's getting harder, but the next race they will all turn into retards.
I think it's a nice game, not sure if it's worth $50 since they really didn't put much effort into it. It just doesn't offer much in the way of challenge if you are already familiar with bike games like EA's Superbike or THQ's MotoGP.
That's really the games major pitfall. There are fewer racers on track than even GT, and everything has a rolling start with them spaced out enough that you never really feel like you're competing. Take for example a race I had at Motegi last night. Firstly, Motegi is the most boring track ever devised so it wasn't helping my enthusiasm much since I was already tired. I must have dumped it three times falling asleep and I still managed to take first with about 5 seconds to spare from the number two bike. Third and fourth bikes were so far behind I didn't bother to wait for their times.
I hope we see a Tourist Trophy 2, but only if PD stops ****ing around and gives us some options for making the AI smarter/harder instead of the usual robot inspired GT AI.
Also it wouldn't hurt to see them beef up the physics so it actually feels like the tires are making contact with the ground in some meaningful manner instead of the bike just floating on some algorithmic cushion directly under the bike.