The Navajo could best be described as a robust workhorse.  It is a satisfying aircraft to fly if flown  well, and this durable design serves operators well.  From a pilot's perspective it is a pleasant albeit noisy aircraft  to fly.  Flight deck noise levels are quite intrusive at even moderate power settings and few choose to operate the  Navajo without the use of headsets. 

The Navajo is a durable aircraft capable of operating in and out of even unimproved runways, and a favorite for charter and corporate flying. It's large cabin, fuel economy, and visual appeal make it a favorite of pilots and passengers alike. The Panther conversion increases climb and cruise performance over the basic Navajo.

Colemill Enterprises of Nashville, Tennessee and it's conversions to the Panther raised the performance of the airplane even more. The cowlings and long spinners of the stock Navajo are replaced with a blunter nacelle with deeper inlets. New four-blade Hartzell Q-tip propellers are used from the fatter spinners. The Zip Tip winglets provide additional lift, more stability, and reduce yawing effect in rough air. The Colemill conversion has been well-received by pilots and passengers.

Aerodynamic  improvements and improved sound insulation, and cabin sealing being two areas of interest. The basic airframe offered  considerable scope for comfort enhancements especially as the airframe aged.

Although it has been out of production for almost twenty years, the Navajo remains one of the most sought after twin  engine general aviation designs of all time. It has been the focus of much attention and design enhancements by third party remanufactures.

Several very interesting videos on several of the Navajo variants are available here: