Contre Jour and Osmos. Neither are free but they are both have great soundtracks. Not fast paced either. Great way to relax. You want to kick ass, get Slayer Pinball.
That's why you pay the .99. Well worth it to me not to have ads. What kind of games do you like. I see you mentioned Army of Darkness, IIRC that's kind of like a tower defense game like Zombieville USA. Might also want to check out Age of Zombies, if we're staying with the zombie theme. lol