I've visited Regal Cinemas in Jack London Square numerous times. The atmosphere is peaceful only if you go on weekdays. On the weekends school children run amok in the theater. The theatre is a bit on the small side compared to others but you feel right at home.
Beautiful old-timey theatre with slightly below-market admission prices, an organ played before peak Fri and Sat shows on the big screen, and frequent political statements on the marquee.
It's a decent theater, but I'd much rather go to a AMC or Century theater. It's just a bit too cluttered inside and not enough show times.