I see conflicting answers all over the place. I want to build a custom setup using the Pi as the brain. I'm mostly interested in beat 'em ups like TMNT or X-men, some 2D fighters like SFII (or SFA2, if that's possible) and Neo Geo games in general. I've heard tons of conflicting answers about this from 'runs bad, use a real computer' to 'works fine'. I'm not afraid of overclocking or things like that. I'm likely going to buy a Pi to play around with even if the information is that it won't work well for my purposes, but I'd like to know before I start putting everything together since it will probably affect the aesthetics of my build. Thanks for the information.
I can only answer for genesis and MAME roms, both of which I've had great success, although one of my fav's - MK3 I haven't successfully run on either yet.
If you run it at 480p resolution and overclocked to 900mhz or 1Ghz I have run Marvel Super Heroes, Marvel VS Capcom, Playstation Games, Metal Slug, and other NeoGeo titles quite nicely. There are plenty of videos on YouTube of people running emulation on their Pi.
On the subject of overclocking, I have a "Made in the UK" RPi model B and had no problem over clocking it. A friend of mine has a RPi model B that is a knock off and he can't even boot when he tries to OC it.
I think the Pi is great for emulating a lot of games. It should run NES/SNES/Genesis no problem. It runs a lot of MAME games just fine, but there are definitely a lot of games that it will not run (very well, or at all in some cases).
For the most part, it is perfectly fine for emulation. I play SF2 on mine all the time. However, for a more serious project, if you want to run newer games/etc. then you will probably need to use something else.
Thanks guys. I'm really only interested in running games up through the Neo Geo era, with maybe a couple of the newer 2D fighers if they work, like Street Fighter Alpha 2.
I'll build for the Pi and just adjust later if I need to change things.