Woah there, lets finish this game before thinking about making future games (:
I like the map to say the least. But there is details that I want to point out.
Star already said that travelling will be dull and boring, and I agree. What I would do is make each part unlockable by a quest as to kinda ease in the bigness of the city. That way you don't push the player into thinking that they are going to dread going through this city for every quest. Also make it sort of like his HQ, where he goes to get his quests and missions. That way there is an actual purpose to going there besides side quests and what not.
Another thing I would suggest is editing that tileset. I mean it's as simple as changing the hues of the roof to have different houses. I mean look around your city, I doubt everyone has the same color roofs. That would get old fast. Also combine tilesets to have different buildings that flow together. I mean don't combine the port city with this one. But maybe the church so you can have a good looking church, etc...
I know you weren't working on the little moat thingy on the outside but honestly, that brings this map down a lot. I would do something different, like maybe castle walls or a plain on the outside. Or even a forest, idk... Just something else, or you could improve on it.
Now onto the castle royalty part. The castle itself is good, but the garden needs a lot of work. Castle gardens are suppose to be very eloquent and sophisticated with lots of different plants in it. Not just a bunch of small trees and a little flowers. What I suggest is looking for a custom tileset that someone made for a greenhouse(I think it's on
rmrk.net or something) and combining some of those plants with the castle tileset and give the person credit of course. But that way you can have an array of plants that flow together and give more life to the castle.
I know this is in the event layer and I can't really tell where your events are but make sure your using a fog and a custom tint (either from ATES or one you made). As this really gives the environment it's feel. I mean imagine walking into a mysterious graveyard with a fog but no tint. I mean that would seem out of place. Also the town square is a little small, I mean normally it's big enough for 50-60 people to walk around on days to see performers, buy their food, or sell things they make. At least that's how it was back in the old days. I suggest maybe making it a bit bigger so you can have those special days.
Just suggestions and critique. Hope this helps at all
(Now that I come to think about it, I believe DeathLock made the Greenhouse tileset as a request shop type thing on
rmrk.net, so look there. It might not have been him though, it's been forever since I've been on
rmrk.net)