Tough to find!
The combination of tweaks on the bikes and tweaks on the riders is an excellent twist to the GT4 model; it reflects the fact that a good race is a combination of bike _and_ rider _and_ player skills, which has the kind of endless, RPG-like fun of GT4, taken to the next level.
The graphics are gorgeous, and yes, as is really the case with serious racers, it's you against the track more than anything else. Mastering the track, and shaving microseconds off your best times, with the rewards that come from that when you get good, is the essence of this game.
As with all the previous Polyphony Digital games, the power of TT is that you can count on the developers having balanced the thing intensively, and well. Your attention to detail as a player will be amply rewarded in this game.
More info: played it a lot this weekend, comparing it closely with GT4 (which I've had since it came out).
This is a better game, in many ways. It's more focused, the bike physics are more distinct per bike, the challenge is extremely varied, and the overall experience is exhilarating.
If you've really dug into the many courses in GT4, you'll have the chance to get a radically different take on them in TT; Laguna Seca, for instance, my favorite, is a wonderful course for motorcycle racing, particularly for the power-bikes.
As with GT4, time spent honing your skills is the best part of the game; you'll really start to master the subtleties quickly, if you pay attention. Along with that, the info on all the bikes is superb, and compared with GT4, again, the tuning options are just what you need to make sense of each bike. Even more than with GT4, time spent tuning your bike for a particular course is critical to your success; you can easily take the bike from unmanageable to finely-honed with the right tweaks of bike and rider.