I can't speak to any of the restaurants at Universal, but we've enjoyed several of the themed restaurants at Disney World (I will mark our favorites with a *). In no particular order:
-Biergarten in the Germany pavilion in Epcot*
-50s Prime Time Cafe in Hollywood Studios*
-Sci-Fi Dine-In Theater in Hollywood Studios
-Ohana at the Polynesian Village Resort
-Be Our Guest at Magic Kingdom (though the service and food weren't stellar, the themeing is on point
-Tusker House at Animal Kingdom Park*
-T-Rex in Disney Springs*
-Raglan Road in Disney Springs*
Hope this helps!