Wasn't referring to the dynamic range of the sound, but rather the accuracy of the engine noises. GT5 sounds synthesized, v8's don't sound like v8's, V6's don't sound like V6s.
With Forza 4 and even in Forza 1 you can identify the engine type in an instant by the exhaust note. Some people think I'm nuts, but I pay ALOT of attention to the exhaust notes of cars. I can identify V4, I4, I5, I6, V6, V8 (flat and cross plane), V10, V12..... At idle exhaust noises can be faked, but at full song each type of engine configuration and even the firing order produces a very different exhaust note.
Can even pick out the W engines like VW'd W6 and W8 engines.
In the GT series games the exhaust notes are very generic. In Forza they put EACH car on the dyno and record them from many different points around and in the cars. They also record the way different modifications change the engine noises. Its a stab at realism that draws me into the games.
I agree, although i think there is a lot more to GT5 that makes it a lot better than forza... such as handling. It is much much better and much more realistic when using my G25. I can live with the sounds.