Simple games have never been out of fashion. Pong makes a comeback on mobile phones, breakout too. And heavy Javascript allows simple but truly addictive games in your Web browser.
Take this game for instance. Found via del.icio.us I spent atleast… oooh, three minutes playing it.
Now have a fuzzy computer speech synethesised voice say “Another visitor… stay a while…. stay forever!!” bellow out before you play and I’m hooked.