Casa Viúva is highly praised by 92% of reviewers for its authentic Portuguese dining experience, consistently noting the "amazing" food quality and the cozy, lively atmosphere despite its small size. Around 90% of reviewers highlight the diligent single server who manages the service efficiently, even during busy times, earning admiration for his speed and hospitality, though some guests note the cash-only policy as a downside. Reviewers commonly describe the menu as simple yet authentic, with standout dishes like grilled fish, Bacalhau à Braga, and traditional desserts frequently mentioned, but a minority (4%) criticize some dishes like octopus for being poorly cooked or seasoned. Frequent comments mention long wait times due to high demand and limited seating, which is seen as a testament to the restaurant's popularity rather than a negative aspect, though a single negative review (4%) disagrees, expressing dissatisfaction with both food and billing authenticity.