I just read al 26 pages of this thread... and I am surprised at how different my perspective is. Perhaps it comes from being an old-timer software developer. Back then software quality expectation were a lot higher. Bugs were not just things that crashed... they included flaws in usability, design, and in general anything that "felt wrong". Having said that... here are my 2cents.
Coding bugs... I have not encountered any. Good job. But I bought the game around June 2005, so maybe the bugs that others talk about were already fixed.
Overall playability... still the best racing game I ever tried.
Design/usability/enjoyability flaws... lots, even some things that were (only in my personal opinion) done better in GT3. Then again, none is really fatal - if you are patient - but they can sometimes be frustrating. I list some, only as suggestions for improvement in a future version. They should all be easy to fix/improve and are based on very high expectations - I am not really complaining about them, so please don't flame me.
- AI is not very smart... probably caused by PS2 processing limitations. Collision avoidance and passing are the areas that need the most improvement.
- Sense of "what to do first, what to do next" is horrible in GT4. GT3 was much better at this. GT4 has many more races, so added complexity is natural, but for a starting player it is just very weird. For example, if you have a B license there are tons of races... if you know where they are. Some are even in the Professional hall!!! That sure was a surprise.
- Manual. Too skimpy. To keep cost down, a full-fledge on-game manual would do wonders. Even better if it was also available on their internet site as a downloadable and printable PDF. I read about the wonderful Japanese manual... this would allow doing it cheaply for all markets.
- Prize cars. In GT3 it always felt like the prize car was proportionate with the race difficulty. In GT4 sometimes you get great prizes from an easy race, or lousy prizes from difficult races. The worst is when you get an "unusable" car - very frustrating. I suppose these unusable cars might have been done as paid advertising or maybe they were considered "cool" by someone. A compromise (maybe for GT5) would be to give these useless cars as "bonus" prizes, in addition to the normal ones. Turn an annoyance into a benefit
- Rigidity refresher cost should be proportional to the cost of the car. For many cars it is cheaper to buy new than used + refresher. This is silly.
- Race difficulty for single-brand races seems to be disconnected from their licensing requirements. I found myself beating almost all of them easily, regardless of license, after doing the exact same set of basic upgrades (tranny, brakes, suspension, tires). I'd think that races that require a higher license should be more difficult.
- Licensing tests are utterly out of proportion to the difficulty of the races the tests qualify you for. Ideally, when your skill reaches the point that you can pass a license, you should be able to place 4-6 in most races for that license, win a few of them, and gradually improve your skill as you race. By the time you beat all the races for that license you should be at a skill point to pass the next license. In the current model license tests are way too hard, and once you beat a license you are usually good enough to beat all races of that license level (and often the next) quite easily.
- Penalty system: Great idea, poor implementation. You can only have a good penalty system if it applies to all cars equally... including the AI. Which is why so many people are frustrated at it. But that cannot really be fixed until the AI collision avoidance is improved. I really look forward to those 2 fixes... today people (including me) drive way too dirty to compensate/payback for the AI's behavior. Once the AI is fixed, it would be possible for every collision to cause a penalty/damage to both cars involved, and truly encourage clean racing.
- Network games: I really bang my head against the wall on this one. It would have been so unbelievably easy to extend the LAN game option to play over the internet. All that was needed is a screen to enter the IP address of the "host" player (instead or in addition to the current automatic-find in local LAN), then use the functionality already built into the game. What a missed opportunity... this game would have been unbelievable for multiplayer over the internet.
Still... even as it is today, it is a great game.