BACKGROUND Online reviews provide unsolicited accounts of health care experiences and may complement conventional patient-experience surveys. However, analyses based on overall sentiment can obscure the specific service domains discussed, while aspect-level approaches require distinction between detecting an entity and attributing sentiment to it. OBJECTIVE This study aimed to characterize service entities and lexical discourse patterns in online reviews of a regional public health care system, compare primary and hospital care, identify where negatively rated feedback was concentrated across facility types, and evaluate the lexical detection instrument. METHODS We conducted a retrospective observational analysis of 47,589 Google Maps reviews from 812 publicly funded health care facilities in Andalusia, Spain. Six service entities and seven complaint- or praise-related lexical markers were detected using a prespecified rule-based lexicon. Sentiment was assigned from review-level star ratings. Negative review burden was defined as the proportion of all reviews that both mentioned an entity and received a negative rating. Lexical-marker differences were estimated using facility-clustered logistic regression within sentiment strata. The final lexicon was validated against manual annotation of 400 reviews. RESULTS System/Management was the most frequently detected entity (42.6%) and had the highest negative review burden overall (37.3%, 95% CI 35.1%-39.5%) and across all nine facility types. Among negatively rated reviews, access-barrier formulations were more frequent in primary than hospital care (12.5% vs 2.2%; OR 6.47, 95% CI 4.57-9.15), whereas waiting-and-delay formulations were less frequent (5.6% vs 12.0%; OR 0.43, 95% CI 0.37-0.51). Among positively rated reviews, professionalism showed no statistically detectable difference (OR 0.99, 95% CI 0.86-1.13), while gratitude (OR 0.45, 95% CI 0.38-0.54) and humanistic-care formulations (OR 0.33, 95% CI 0.25-0.45) were less frequent in primary care. System/Management burden was highest in outpatient consultation centers (52.5%), health centers (46.0%), and local health posts (36.2%), forming a descriptive pattern of higher burden in ambulatory consultation settings. Five of six entities achieved precision between 0.91 and 1.00; Facilities showed insufficient validation performance and was excluded from substantive interpretation. Lexical markers generally showed high precision but limited recall. CONCLUSIONS Online reviews revealed distinct patterns in organizational, access, waiting, and positive-care discourse across settings. Organizational processes showed the greatest concentration of negatively rated feedback, particularly in ambulatory consultation settings. These findings describe reviewer discourse rather than population-representative patient experience or entity-specific sentiment. A transparent, empirically evaluated lexical approach can provide a reproducible means of identifying domains of negatively rated feedback warranting closer organizational investigation.