Depends on what you like but here's a couple of casual non fine dining places in Tallinn: Da Rocca (homemade Italian food), Argentina (there are two, go to the one in Sikupilli, very few tourists due to the location), La prima (great pizza, around the corner from your mentioned philly joe's, reservation needed in the evenings), Also check out Telliskivi area and Noblessner area. For a quick bite, check out Balti jaam street food "street".