1. I know most don't like the OEM stereo. I really don't want to change anything out, so don't waste time with "It sucks upgrade"
2. I've seen where the Bose system in the newer G's got softer.
3. I had a 2004 G35 sedan and that system runs circles around this one. My 2002 Altima, with a "middle of the road" OEM system sounded better.

The issue. The thing literally sounds like a tin can. I have the bass & treble to the right. I does sound a tad better, not really a lot, if I have the Driver Immersion Studio(whatever it's called) turned off, only thing turning it on does is seem like make the volume louder, no real "sound" change. I have the speed sense all the way to the right, and it doesn't seem like that does anything either. In the G35, there was a big difference in volume from standing still to rolling.

Can the amp be bad? Seems like all the speakers are working. It just has zero kick compared to my G35 or Altima(again wasn't even a Bose system)

Any ideas?

I'm not impressed at all with the sedan stereo. The coupe sounds so much better. First, go through the car diagnostics and make sure everything is properly functional:

http://moodym.com/articles/diag/hidden-diag.shtml

Otherwise you can upgrade the tweeters (they are 4ohm) and I think the mids as well...those would not be too costly. Bass? good luck.