I gave the demo a go. I didn't spend an enormous amount of time looking for secrets, so I may have missed some things. Here are my initial impressions:
+ I think you did a good job incorporating sample maps and making them your own. I do think you're going to need to start making custom dungeons in the future, though. This is particularly noticeable when the world-ending dragon statue isn't the center of room, but just seems to be tucked away in a corner. I'd argue mapping's one of the most time-consuming parts of a project, but your project is good enough to warrant the effort.
+ Overall, the writing is really quite good. I like the characters, am happy with the tension between them, and am curious to explore them and their dynamic more. They aren't a cast that invest a whole lot into The Power of Friendship, which is refreshing. Each character has a distinct vocabulary and speech patterns. I'm really loving that the core concept of the game is these three characters trying to profit off of a mistake they make. Dialogue is organic.
+ Given the limitations of the vanilla engine, you do a good job with cut scenes. I'm inspired to try and follow your example.
- Witch battle is too easy. Don't be afraid to challenge players a little more. All our potions and scrolls are just taking up space if we're not given more motivation to use them.
Bugs: The big monsters guarding the stairs don't end the game, but simply disappear when you touch them.
There's a small graphic glitch immediately before and after the witch battle, where Aaron appears off to the side.
Church revive effect is a bit wonky. I'd go for something smaller centered around the character.
Grammatical errors:
"Owner of one of the worlds few Airships." Worlds should be world's.
"Now, where could she has run off to?" Has should be have.
"You must be desperate for a lay if your proposing that." Your should be you're.
"Did we suddenly become to do-gooder party?" To should be the.
I also noticed you seem to emphasize important words by capitalizing the first letter. I'd recommend using text effects, instead.
Plot holes: I may have simply not been paying attention, but when you first arrive at the witch's castle, Ian admits he doesn't know what they're looking for. Then after you beat the witch, he's excited to have attained the star mirror, indicating he *did* know what they were looking for.
Food for thought: The motivation for searching the tower for valuables stems from the royal messenger short changing Ian (by as much as a fifth of what he originally promised, according to Ian's math). Given that the conflict of the game seems primarily character driven, I'd argue that this is a tad weak. The cast lets the monsters out, setting the plot's events into motion, and so I think it should be the cast that necessitates the trip to the tower in the first place. Maybe have Ian squabble over the price with the RM, or insult him in some way, thereby screwing himself over. Again, just food for thought.
Overall: I'm really impressed with this demo, and am looking forward to more. Writing is your strength, and I recommend using it to its maximum effect.