I'm going to put this post in the second-chance queue [1] because, like I said, it seems like the community may find it interesting to discuss, and also the project hasn't had much discussion on HN for a few years. But please avoid this kind of thing in the future!
I decided to start developing a 3rd-person MMORPG using Babylon v4.0 as a side project, however after investing far too much time and getting it to a decent point, I came to question why I was bothering with a strictly web-based engine for a rather complex and extensive game. If I was going to go to the effort of creating this game, why not use some kind of game engine that can then export it to multiple platforms including web? So since then I've halted dev on the babylon version of the game, and begun porting to the Godot game engine, which can export to web among other platforms.
With all that said, I still enjoyed my experience using Babylon, it was just the wrong tool for my chosen project.
Babylon is a great choice for a lot of web based 3d content, but if you're intending to build any kind of significant game I'd recommend using a proper game engine from the start as it will enable you more flexibility in the long term.
If however you do require a character controller for Babylon, I used babylonjs-charactercontroller [1] for my project and found it dynamic enough to work for most situations.
[1] https://www.npmjs.com/package/babylonjs-charactercontroller
