Have been using RetroPie running on a Raspberry Pi 3 since the summer of 2016. Must say it was pretty easy to set up and use. The only problem I had back then was getting my PS3 controller to work wirelessly. Have some searches on YouTube got it working. Well the other day decided it was time to update to the newest version of RetroPie, versions 4.3 . You can got this through a menu screen. For some reason it didn’t work right. So decided to start from scratch.
It is even easier to setup now. All so every impressed at how much faster it runs and looks. All so even easier to get a PS3 controller setup. Found a step by step which works perfectly. You can read how > here. Scroll down to the heading, “Using the RetroPie GUI to configure the PS3 Controller Bluetooth Connection”
GetBent57 