it's an aggressively mediocre system that's had years of a huge community polishing it to a mirror shine.
You can praise it for the community content, or go off-book like you can with any other system, but that's applicable to any system with the same community size.
Whatever you look for in it it's lacking in comparison to another system. Tactical combat? PF2e. Rules light? Worlds without number.
It's a decent middle ground of a system only because of community hard work. But that's only for the GM side. Players still need to deal with the poor character creation, unless they get a lot of support from their GM.
Can you explain why? It's fast, sure, but it's simultaneously the most important character design choice you can make and also cripplingly absent of actual choices.
Rather than front-loading decisions in character creation, you get a bunch of more interesting choices to make at each level up, including an elegant multiclass system. In other systems, I feel like the only interesting things you get at level ups are just a few points here and there, and you already made all of your most important choices in the hours you spent creating your character. In 5e, just about every time I level up, I feel like I found a new gear to shift into. As a Fighter, for instance, there are tons of interesting choices to make at level 3 just within the Battle Master subclass, let alone other subclasses. The 5e rules sure aren't perfect, and I definitely haven't sampled every RPG system out there, but given that they all had old D&D rules to learn from and solve problems within, I think 5e solved a ton of them in really clever ways compared to others that I've tried. Character creation is just one of them.
Many classes do not get any choices at many levels. Sometimes the choices are thin.
Also calling 5e's multi classing system elegant is extremely generous. It works, some of the time, but it's extremely prone to making weaker characters with the occasional high power interaction.
Fate is an elegant system.
Also class-and-level is only one way to make a game. You could just not do that and open up whole new worlds.
Many classes do not get any choices at many levels. Sometimes the choices are thin.
True. But I'm also playing with Xanathar's and Tasha's, and with a choice of so many classes, you tend to gravitate towards the more interesting ones, so if one class is a dud, it doesn't weigh too heavily on the game when there are more interesting choices available.
Also class-and-level is only one way to make a game. You could just not do that and open up whole new worlds.
You can, but it's not an inherent downside to have classes like this either. The things they're allowed to do and not allowed to do create some clear strengths and weaknesses.
In comparison to other games I've played I find this the opposite. Proficiency and ability scores basically never change after creation. And level ups allow for very very little decisions and distinction other than class.