The reason why the level of enthusiasm is so high is first and foremost because of the capabilities of the program. Right after installing it the amount of tools and functions at your disposal is vast. Once you start adding plugins the amount goes from vast to near limitless in a hurry. Properly configured its abilities are near unmatched in file management on any computing platform ever.
The second reason is of course because of Total Commander's author. His vision of what a file manager should be started well over ten years ago and that he has been able to keep his code-base well-maintained to the point that even now ten years later he's able to add new features with ease to his code should be a testament to his programming ability. He, unlike other file manager authors, takes a very keen interest in what his users think weighing each suggestion they make very carefully rather than just dismissing it out of hand like other authors.
If you commit to learning Total Commander's power you may find yourself with more hard drive space as you uninstall programs because you no longer need them as TC does it as well or better than those stand-alone apps.
The only file manager that I can think of off-hand that rivals TC in features is FAR as it had huge amounts of plugins available for it as well, but it has been abandoned by its author last I heard.