My first impressions of "Dragon's Secret" on first watch were mostly very positive indeed. There may not have been much original about the story, but it was fun and clever enough, the setting is used beautifully and the episode captivated visually. 'Scooby Doo: Mystery Incorporated' really impressed me as a show just over a decade ago and is still one of the better and most different Scooby Doo shows. And this is coming from a big lifelong Scooby Doo fan, who has liked most of the incarnations.
"Dragon's Secret" is still a very good episode twelve years on. It is a slight let down after the outstanding "Escape from Mystery Manor" and is not one of the best 'Scooby Doo: Mystery Incorporated' episodes in the way that that episode was, but there is a huge amount to like about it (the best elements being excellent) and not an awful lot to criticise. If one is wondering what 'Mystery Incorporated's' appeal is, and there may be some as there are Scooby Doo fans that don't care for it and will have told them so, "Dragon's Secret" is a very good representation of it even if not the best.
Will admit that the identity of the perpetrator didn't surprise me all that much, despite the ending being clever.
Also feel that there could have been less of the Shaggy and Velma plot, that was going into soap territory and have never cared for how Velma was written in this subplot which always came over as mean spirited and shallow.
However, "Dragon's Secret" is very well animated with some of the more imaginative visuals of the show up to this point. Especially on the jade dragon. Who is very cool in look and has a great sinister personality. The music is not discordant with the action and doesn't come over as overdone. The characters are well written and interesting, with the only serious reservation being with Velma which was a general problem this season. The voice acting is excellent all round.
Furthermore the writing is smart and thoughtful, with lots of intrigue. The story may not have many surprises, but it is intricate and clever and things are progressing very nicely and makes one eager to know more. The mystery always intrigues and entertains with a good creepy atmosphere. The cultural aspects are done tastefully.
Concluding, very good if not incredible. 8/10.