I don't know about you but I love the sound of wind blow through the trees, birds chirping and the absence of trucks driving on the highway. The ambient sounds of nature are beautiful and amazing. They are also missing from Minecraft for the most part. Sure we'll hear a chicken call or a pig oink but there is no wind unless it rains. When I'm deep in the earth near lava I don't hear the pressure behind the rocks. I want my world to be alive, not just with animals and people but with sounds.
This first mod pack does just that, adding the beautiful ambient sounds that are missing from the game. I can't say they got everyone right but it's a nice change. Sometimes you don't notice these touches are gone till you hear them. It breathes a new life into the game that I honestly feel is needed down the road on a official level. Specially with all the biomes changes in the pipe. Take a listen to MAtmos an atmosphere generator mod and check it out for yourself.