I buy cars for their performance and moddability (and this car is very moddable having the Supra's 2jz and all), but I'll rate this car from a consumers point of view, since you are probably interested in buying this car. This is not your average type of Lexus. Lexus' are usually known for their comfort and amenities, but this car is different. The IS 300 was designed to compete with the 3 series, and that it does. This is a SPORT sedan, so it drives like one, do not buy this car expecting the usual laid back handling of the other cars in the Lexus fleet. This is definitely the car to buy, if you are looking for a RELIABLE car that will add some excitement to your daily commute to work.
Moddability. The 6 disc in-dash CD changer is nice. But my favorite feature of the car is definitely the handling. It drives like a true sports car should... fun. And of course there is the fact that is a Lexus, the definition of reliability.
Being a "sport" sedan the car could have had more power, but it's decent enough. The dash is made of some extremely cheap plastic, that not only scratches very easily, but has a talent for showing dust unlike any other material.