I put together a retro pie a few raspberries ago just to play around and it was pretty cool. It was a bit touchy at times and i was more annoyed than i thought i'd be that it didn't have an on/off switch or a shutdown command. I've heard the new version is pretty awesome, especially with the modding community localizing stuff, making translation patches, etc.
I still bump up against the legality of it all... It'd be awesome just to google a title, download an iso or a rom or a bin, pop it onto a usb and play, instead there's all this copyright law, and debate whether or not I'm allowed to circumvent protection to back up items i own. It's been a while since I've kept paid attention to the emulation scene, so it may be different now.