FEW TELEVISION shows have managed to captivate audiences in quite the way “Game of Thrones” has. The first episode of the current season reportedly drew 17.4m viewers—impressive, given it is hosted by HBO, a premium subscription service. In contrast, the first episode of the final season of “Breaking Bad” attracted just 2.9m viewers.

Yet, although “Breaking Bad's” last season received almost universal praise from critics, fans are unlikely to hold the final season of “Game of Thrones” in the same regard. Reviews on IMDb, a repository of television and film reviews, show that the most recent two episodes of the show received average ratings of just 6.1 and 6.7 out of 10. Those numbers are far below the average for the show's previous seasons. The lowest rating any episode received prior to the current season was 8.1.

What went wrong? Fans have offered a number of theories. One is that, though the show's authors are brilliant at adapting other peoples' work, they may be less adept at writing original screenplays. The first six seasons of “Game of Thrones” were based on George R.R. Martin's “A Song of Ice and Fire” series of books, but the last two seasons have been based on their own writing. Another possible reason is that the authors simply did not give themselves enough time to work on the project. The final season of “Game of Thrones” is just six episodes long but needed to resolve a lot of plot points. Some fans wonder about the writers' commitment to the show, noting that they have recently received a lucrative contract to work on a new Star Wars film.

Few have high hopes for “Game of Thrones'” final episode, which airs this Sunday. Punters on betting markets reckon the episode's rating on Rotten Tomatoes, another television-and-film review site, will probably fall below 64.5%.

The show's decline is not without precedent. Data from IMDb show that at least one prominent show has had a harder fall: Netflix's “House of Cards”. The series, originally based on a British drama from 1990, suffered immensely after the unexpected departure of Kevin Spacey, the lead actor who had to be removed after being publicly accused of sexual harassment.

The final episode of “Game of Thrones” seems likely to leave millions of fans feeling unsatisfied and angry. But they should take solace that it could have been a lot worse.