I understand you’re quite comfortable with Java2D at the moment. I was like that with Slick (an outdated game library). I decided to give libGDX a shot only last summer and while it’s definitely more powerful, it in turn is much more complicated (I still don’t understand the Camera class :-X).
I suggest you keep going with something you’re comfortable with, and maybe on your other time try to re-create an older game of yours to libGDX or some other library. LibGDX is basically a kind of wrapper for LWJGL to make it more understandable.
Good luck! ;D