For real though, it's crazy how easy it is. I found my original Pi buried in some old stuff and was just like 'screw it, I'm going to do something with this' and then I was playing Pokemon Yellow that weekend. I've been working on the design for a cabinet for a little bit, but haven't had the chance to build it yet:
If I may add - do yourself the pleasure, and use a standard usb Xbox 360 controller, otherwise you are in for a world of pain. I've tried a NES30 controller over bluetooth and after a week of trying different configurations nearly chucked the whole thing in a bin. Also some of the emulators are too slow to be usable, even on the Rpi 2, NES and SNES work absolutely fine, but MAME, N64 and Dreamcast are more like curiosities, very few games run at anything even close to full speed on them.
Actually, for N64 emulation, I have a 100% full speed fork of Mupen64Plus for the Pi 2 sitting around on my hard disk that I hacked together a while ago. I should really clean it up and post it to GitHub.
There's no fundamental reason why the N64 can't be emulated at full speed on that hardware. The VideoCore IV blows the RDP away in fill rate, after all. It's just that the available video plugins are old and aren't optimized for mobile GPUs. Additionally, Broadcom's drivers have a tendency to stall in inconvenient places and the emulator needs to work around that as well. But once those are fixed, most of the popular N64 games run beautifully.
...Which is sad. I played Mario64 in Corn on a 400MHz K6-2 around Y2K. Nemu+1964+Project64 each handled more, but it seems like I had to wait for my Athlon XP before my machine was fast enough to be useful.
Good emulation is hard, especially when you're dealing with code that was built around the bugs, quirks, and timing issues that the original SNES authors had to deal with. Then you have to worry about buggy software that works because of undefined behavior [1, see Speedy Gonzales]. More recent emulators have focused more on correctness than speed, because it means less work trying to patch and hack around broken games.
I completely agree with this. If you do choose to use a wireless Xbox 360 controller, make sure to get an official xbox controller wireless receiver. My wife purchased a knockoff for ~$7 and I spent a couple hours trying to get the controller to sync. Using an official controller, the drivers with emulation station just worked and I was up and running in five minutes.
I have the SNES30 and the SFC30 working great on my rPI2 - with retropie 3.5, you just have to make sure to create the UDEV rule, then it works like magic.
If you have a Raspberry Pi sitting around that you don't know what to do with, just do this. You won't regret it.