a site that completely bypasses the whole "download, install, deal with it" part of the old console days and moved everything into the browser. http://gam.onl/
it has a pretty extensive archive ranging from ps1 to nes, sega to arcade. you click, the game opens. it handles the emulator + rom business in the background, and all that's left for you is that nostalgic "just one more round" feeling.
of course, the copyright side of things is a bit of a gray area, and you might run into ads/pop-ups, but as a concept, it's a lazy gamer's dream: no installation, no config, straight to the game.
in short: your childhood, in the form of a chrome tab.