I couldn't be much happier right now. Considering how much difficulty I had getting PiPlay off the ground (and after all that it never even flew), this has been a dream. Everything works! No wrestling with config files, no downloading special drivers, nothing. It. Just. Works.
In the preliminary stages I plugged in my Mayflash joystick as a controller. That proved to be inadequate on its own. Alongside a PC keyboard it was fine, but I wanted it to be even simpler than that. The PS4 controller I borrowed did the job, but seemed ill-suited to the task.
Today Amazon delivered a pair of SNES-style controllers, so I immediately hooked one up and took it for a spin. This sucker is PERFECT for the old console games! Not so much for the arcade stuff, but Atari 2600, NES, and SNES? Fuhgeddaboutit!
All of this has made me wonder if I should rethink my retro gaming plan. Maybe what I need to do is get a second Raspberry Pi (probably a Zero) and dedicate it to the arcade side. It'll be simpler that way, controller-wise, I think. Maybe. We'll see. For now, though, I'm focusing on the old console side, trying to get it as smooth as possible. We've got a family reunion coming up this summer, and I would love to have at least one RetroPie rig ready to roll by then.