I have done game emulation on an RPI2 and RPI3, i used emulationstation / retropie and found games above 5th generation (ps1, n64, dreamcast) do not play well. Once the RPI has a better GPU i expect that to change. But for GBA/Genesis/SNES and others its alot of fun and very nostalgic.
RE: RetroPie Videogame System