I don't really do gamedev, but this was a fun thing to try. Heres a shitty game + game engine I made back in 2017 (or 2016 I cant remember, it was for Ludum Dare 38). A friend did all of the art.
(also this isnt 3D, but don't tell anyone im breaking the thread title)
The wide open scene

tile/scene object culling view

This somehow runs ok on my p4 xp machine & the steam link natively because of my caffeine induced high of ~4 days of straight programming. I will never forgive the TMX format for being XML. Trying to make the worlds worst TMX parser in a few days almost killed me. It chops off the rightmost tile column for whatever fucking reason as well, so you have to add garbage tiles at the right side of every level.
Then I tried my hand at a really shitty 3D game engine last thanksgiving and I'll never finish it. I was trying to use ODE2 for physics, but the thing is its collision detection system is the dumbest approach ive ever seen. You control the collisions and I don't have the energy to flesh out some general collision system for it so that 3D engine is forever dead. 2D forever for me I guess.

Then the stupid virtual game variable system was a cluster fuck. Does garbage collection at every state change though (and iirc when you manually set the unused flag).

(also the forum ate my reply and I had to rescue it with the firefox http monitor :( )