I have the exact same problem. It is way too quiet, I can hardly hear it ringing or if I get a text. My other half has the Galaxy S2 we compared volumes and the S2 is much louder, you can hear it ringing. To get a proper idea of the difference we both installed a sound meter app (the smae one) to check the sound levels. We put each phone up to full volume and played the same track (from the same MP3 we transferred onto both our phones), the nexus only reached a maximum of 90 decibells at the absolute height of the song and even then, the 90 was rare, it was more like 85. When my other half ran the same set up his was maxing out at 100 decibels for most of the time and that was only because the app in question didn't go any higher than that, so soundwise his results were off the chart.
Have you guys got any advice? Is this something that can be fixed? There isn't much point me having a phone if I can't hear it ringing because it's in my bag or under a cushion or something.