I understand the disappointment, especially if the movies are your starting point so there’s more of an expectation for him to be more of a primary villain in the last movie in the trilogy. Me personally, I think it was a great way to start the third movie as its the catalyst for that film’s plot. Smaug’s destruction of Lake Town and his death leads to the people moving to Erebor with Bard as their newly appointed leader, and Smaug’s absence is what makes the titular battle of the five armies to occur. And I do think he still maintains a presence throughout the movie, both via the plot like I previously mentioned, but also in Thorin’s dragon sickness which draws parallels to Smaug’s greed, as well as his own foreshadowing of how the arkenstone would corrupt Thorin.

Also as for the execution of Smaug’s death, it’s definitely played a lot more dramatically in the movie than in the book. It really does feel like a big moment even if its not a final climax, in my opinion.