Why do some Samsung Crystal UHD and QLED models get criticized despite high star ratings?

Specialist communities and buying-guide threads repeatedly warn that Samsung's lower Crystal UHD (U8000-series) and entry QLED (Q7F) and mini-LED (M80H) models lack local dimming, run at 60Hz in some sizes, or use older panels, which limits real picture quality even when retailer star averages look high. The reviewers we read advise cross-checking the specific size and model year, since features vary within a series.