I've been making a game in RPG Maker VX Ace called "Dragon Quest I Remake", in which I take the bare basics of the Dragon Quest I story, revise it with lore from second and third game, then add a lot of original stuff on top, so roughly only about the very core aligns with the original game, the rest is my invention.
However, that doesn't mean it's easy.
Since I only decided to retain the basic core of the original plot, the rough locations of the original towns, and most of the original monsters, the rest I had to import from other games in the series, use community resources and official DLC for RMVX Ace to fill in blanks, or code myself.
As for the graphics, that's surprisingly easy to do. As for coding, since I'm still a noob to Ruby, I'm grateful for all the scripts made by the community, has really made my job easier. However, the hardest part has been making sure it all works as a unified whole.
RMVX Ace is a surprisingly easy program to learn, but mastery is pretty difficult. Add in the fact my game is a largely one man project in which I have to be coder, designer, artist, musician, and director, and I'll admit it can be rather tedious. Most tedious would be the bugtesting, in which I must make sure every element works as I plan it to.
Regardless, it has proven rewarding, especially once I see all the fruits of my labor pay off, and so I plan to continue working on it, though tip for anyone else wanting to make a game: It takes patience, time, and hard work. If you don't have any of the above, then you'll find the difficulties I mentioned above insurmountable.