The main reason why this show should succeed is that HBO has so much experience. They’ve made fantasy worlds including Westworld as well as Game of Thrones. Meanwhile, they made mistakes in the latter GOT series, which taught them many lessons (via Bloomberg).
They received a learning curve as they discovered what works and what fans won’t expect. This new series will have a significant influence on their credibility as a network moving forward. If they don’t succeed they may fall too far behind Amazon and Netflix to be viable in the future.
The main reason why the new show may fail is because of fan ambivalence. Game of Thrones had one of the worst endings in TV history. Fans resented everything about it because they committed to the journey and expected a great payoff. Instead, it felt as though a child wrote the final episode (via Collider).
That’s why many fans may not tune into the show. It’s difficult to invest in something that isn’t trustworthy; unfortunately, that’s how many of them feel right now. House of the Dragon has a lot to prove from the very beginning. However, it’s the ending that’s the problem and that’s what people worry about.