It turns out that setting up a Raspberry Pi with Retropie is fairly easy...
I received my Canakit Raspberry Pi 3 Model B today. After unpacking the box, it only took me maybe 10 minutes to get everything assembled and connected to my TV. It came from a 32GB microSD card configured with something called NOOBS, essentially a beginner's starting environment.
After verifying that the Pi was starting up okay, I went to the Retropie site, downloaded the latest image, formatted the microSD, and copied the image to the card, all as explained on the Retropie web-site. The SD cards is then inserted back into the Raspberry Pi, where it does some self-extracting and configuring. This took me maybe another 10-15 minutes.
I then used a USB stick to build a transfer drive, and copied some ROMs I had for a few systems onto the stick. I then copied over the ROMs. This is all explained on the Retropie site, and took only a few minutes. I then restarted the Raspberrry... and the games started working... but there was no sound!
After checking cabling and making sure sound was turned on via the configuration menus, I checked out the web-site. Apparently this is a common issue, and there was a suggestion to add a line of text to the boot/config.txt file on the SD card. This line forced on some sort of sound setting. I tried this - and now the sound was working!
I've only played with it for a few quick games on a few systems. The 2600, 7800, and TG16 seemed to have very good emulation. With the Vectrex, I found the sound was a tad warbly at times, and I thought the screen resolution was a bit pixelly. I also tried a couple of games on the N64 emulator, and the sound was very choppy, to the point of distraction. About halfway through a loop in Beetle Adventure Racing, the emulator just plain locked up and died. I also tried WaveRace 64, and it was far too choppy to be playable.
I'll play with it more of the next few days. It looks like it does a very respectable job with 8-bit systems, but later systems are going to be very hit and miss I think. Overall it seems pretty decent for what I want - emulating pre-NES systems.