GaN FET Amps vs. Traditional Class D Amps

First you would have to describe what is meant by 'traditional' class D designed amplifiers.

All "traditional" Class D amps do NOT sound the same.  You have to compare specific models.  The devil is in the details.

In general GanFet  ups the ante in terms of performance level possible. Does not mean all GanFets are necessarily better.

I have several Class D amps including Hypex Ncore,  Class D Audio GanFET, and other chip based Class D amps. Have owned "high end" Icepower in the past as well.

They are all good but each different.  The Class D Audio GanFET is the best performer in all regards.  HYpex Ncore is no slouch but sounds clearly different.  That’s just one specific Hypex Ncore amp.  There are many designs  at various price points with different power supplies, opamps used, etc.   You have to compare specific models to draw any meaningful conclusions.  

Buckeye Amps on GaN FET…

https://www.buckeyeamp.com/blog

That blog post by buckeyeamp is your typical ASR tripe. He whines that the GAN transistor shows little measurable improvement over mosfets used in most class d amps. 
 

So what? We are interested in how things sound. Like the OP I too am interested in how GANfet based amps SOUND compared to the usual Class-D offerings.

The limited amount of UCD and ice power amps I have heard so far were all smooth, clean, and lacking realism or lifelike sound the better class A/B amplifiers can achieve.