Just a reminder --- Every plane's sounds are true to life. From the 109-E4 to the Typhoon, you won't hear an arcade-style sound in the entire pack.
Early 109's have the distinct buzz, while later models, especially the G-10, have a much lower tone (although it's not any quieter).
190's, well, sound like 190's. Can't say any more than that.
Japanese planes sound quite nice this time around. The engines are actually pleasant.
The F4U Corsairs have that Pratt & Whitney hum. They're loud as hell --- but that's not bad, since they sound so damn good!
Then we have the fighters equipped with Allison engines. The P-38 has that subtle whirr, and it's unique scream. The P-40's are in a class all their own (the engine choke on the engine startup is great).
Russian planes. They sound as they should: Quirky, low-grade, yet powerful. Very nice for the bare-bones pilots of AHII.
Merlin engines... What can I say? They're quiet, yet loud. The P-51D is almost soothing...
Then, the Typhoon/Tempest. These things are LOUD, but they have that wonderful whirr/buzz sound. It really increases the experience of flying such a plane.
Of course, there's more... Too much to mention, actually. It's all a massive upgrade from other sound packs. Reasons?
Engine scream/hum/buzz/whirr, and prop wash effects. You also get that unique howl from the Ju-87, and the whistle that made the F4U Corsairs famous.
There's lots to look forward to. Lots.