I've been very disappointed with the default music player on my Galaxy Nexus. I have all my MP3s recorded at a very high bit-rate and I use Ultimate Ears TripleFi 10 headphones so sound is very important to me. The default player on the Nexus sounded awful with compressed highs and weird frequency roll-offs. Plus, it skipped a lot which is odd for a digital player. The sound was much worse than out of my iPad which I already view as a compromised player.
I checked around for alternatives and the Neutron MP player seemed to be the most highly reviewed. I purchased it today and WHAT A DIFFERENCE! If you care about music, this is definitely the way to go on the Android platform. I'd forgotten how good my music can sound. The interface is a mess and the application needs to be restarted a couple of times to get all the functionality in there, but it definitely gives the best audio experience I've heard from a mobile MP3 player.