I've been playing this game for HOURS. I love it so much! Currently my population is 8000 with 900 happiness and 3200 gold. I just finished up day 150. I have a ton of suggestions for you!
1) Like most people have said, gameplay for people further down the road. It's gotten repetitive (but it's still fun)
2) I really think that there should be a sort of celebration for 100 days, and people could hold a festival or something that lasts a few days and brings in a lot of gold.
3) While I was playing this, I was really getting the "different outcomes come from different choices" feel. However, it didn't seem to be this way. I think that based on your decisions, different things should be available. Maybe if you constantly are evil to your citizens (through lil fang, chester, etc.), you can have more evil options, and if you do more good, more good options will appear.
4) I think the king should age as you progress through the game, and should die after 200 days (unless more material is added to make people want to go further than that), which leads into my next suggestion.
5) ENDINGS. I actually have ideas for 2 -- both would be where the king dies after a set period of time, but what happens next depends on if you took the 'good' or 'bad' route in the game. If you chose the good one, the screen will fade out as the king closes his eyes, and this light soft music will play. It will show everyone in the kingdom mourning together, then having a farewell festival thing. It could cut to the "Knight" character in the game who always wants to go on quests with an awkward fitting crown on his head, and then finally, it would show everyone together in the kingdom, even Mercury and the tree stump guy, and it would zoom up into a night sky, and fade out into darkness all peacefully and nice like that. For the bad ending, I'm not so sure, but it definitely wouldn't be as heartfelt.
6) I feel like there should be potential war between other towns at times, and that's more where the whole thing about "having more swords" is safe. The king would have to make decisions to lose some population or not based on what he thinks the war needs. It would cost money & happiness, etc., and you might have to surrender 2000 gold if you lose, and if you win, you win 1000.
7) (I really want this) Instead of a huge pile of gold, after every 1000 gold, the 1000 will turn into a "chest" (like a treasure chest) and will represent 1000 gold.
8) I'd love it if the barber actually cut the king's hair.
9) Chester should lose his teeth when you cure him. He should also ask for the king to put the witch into the dungeon for doing this to him, and the king can say yes or no. If not, she'll turn him back into a man-eating chest, and if you do, she won't tell you when to pay offerings. You'd have to 'hire' the ghost who always asks the "trick question" to do the seances for the evil spirits instead of the witches.
10) I'd love to see the kingdom turn into a city over time. Mason could be a much bigger character. And if that happens, maybe clothes on characters could slowly become more and more modern.
11) I'd love to see some pirate characters added into the game.
12) Maybe less 'yes' questions, and more questions that make you think.
13) If the scientists can make gold machines, certainly they can make more things that are really cool and beneficial.
14) I'd like to see more quests for knights to go on.
15) Little timmy needs to come in and ask him if he's seen a "kitty cat" and if you say yes, Timmy will always come into the castle carrying the cat. The first time he does, he'll thank you.
16) All the kids should age.
17) Instead of constantly "the people are happy! The city is growing!" Maybe include some humorous news report or something.
18) Like others have said, a reputation level.
19) Also like others have said, a save game function.
... I just closed out the game.