Polyphony's latest is good, but has untapped potential.
Tourist Trophy basically takes the Gran Turismo formula and replaces the cars with motorcycles. That's right, you're still going to have to head off to the license center before you can really start. The license center is the place where you learn the ins-and-outs of motorcycle racing. The tests you need to pass range from high speed maneuvers, to slaloms, to full-course time trials.
However, after you've passed the licenses, Tourist Trophy departs from the traditional Gran Turismo formula radically.
There are three main ways to win new motorcycles and rider gear. The first is to pass your license exams. The second way (which is probably the one you'll be using the most) is called Challenge Mode. Challenge Mode is very similar to the license center: you pick the bike that you want to earn, and the game gives you a task that you need to complete to win the bike. For example, you might have to overtake an opponent in two laps of the track to succeed and win the bike. This is an easy way to get motorcycles early on, but you'll use it lass and less as time progresses. The third way is to participate in races. Tourist Trophy gives you a list of class specific races that give you the opportunity to win new motorcycles, gear, and race numbers for your bike.
The first impression you're going to get about the game is the graphics. Visually, for a PS2 game, they're some of the nicest looking you'll see. Bikes have meticulous detailing, and the tracks are amazingly realistic re-creations of tracks like Laguna Seca, Le Mans Sarthe, Suzuka, and more. Textures are smooth and crisp, especially when running the game in high definition (Tourist Trophy supports 720p and 1080i). There are a couple minor flaws, mainly in the bike's rear view mirrors, but for the most part the graphics are top-notch.
Another thing you'll notice is the amount of depth the game provides. Tourist Trophy has a decent amount of bikes, around 120, and you can customize their tire compounds, suspension settings, gearboxes, and simple things like that. It's good, but it doesn't compare to the absolute control found in Gran Turismo. However, rider customization is extremely dense. You can change everything about your rider: height, gear, even customize the way your rider leans during sharp corners! You can create 4 different setups for your rider, two sets of racing gear and two sets of casual gear. The gear all comes from licensed companies such as Alpinestars, Spidi, Arai, Simpson, and much, much more.
The gameplay for Tourist Trophy has it's strengths and it's weaknesses. The PS2 can only support 4 bikes racing at the same time on screen, so the field is very sparse. Also, the opponent's AI often rams into you if you're lagging in the straightaways, and makes no attempt to avoid you in any way. Another awkward thing is the collision system. Overall, it's good, but head-on collisions don't register in the game's crash system, so you can slam straight into a wall at 120 mph and still stay on your bike. Also, the bike occasionally bounces wildly after a crash for no apparent reason, and it's significantly tougher to pull a wheelie than it is in real life.
On the upside, the core physics of the racing are superb. A 70-hp Honda will handle completely differently than a 160-hp Ducati, and a 125 will turn completely differently than a 1400 sports tourer. The riders move smoothly through the corners, behave realistically on the ground after a crash, and the framerate never stutters.
The sound quality is very good, too. The menu music is the same old techno-ish keyboard stuff you'll find in Gran Turismo, and all the bikes sound different and very realistic. The in game music selection is alright: there's a few annoying songs in there, but you can turn them off if you'd like. Unfortunately, when you wipe out, the bikes make virtually no sound at all. It really reduces the sense that you're actually hopping the barrier and crashing hard, but for the most part the sound is excellent.
Overall, Tourist Trophy is a game most suited by fans of Gran Turismo or fans of motorcycle racing. It's a very technical game that takes time to master, but it pays off in the long run. My recommendation is that if you're a big Gran Turismo fan, you should buy the game right now. You'll enjoy it. For everybody else out there, rent it first.