If you don't want to hack NES ROMs (which is easier than it sounds), there are a few pieces of software that will allow you to make games from scratch with little to no programming experience. Game Maker is actually really good and allows you to make games fairly quickly: http://www.yoyogames.com/make RPG Maker makes it easy to create games that focus on character interactions and development: http://www.rpgmakerweb.com/
I have an idea for Castlevania 2, but it's going to take a few days to complete. I'm actually working on a custom patcher because I found a way to add new new code to the game. But I want to give everyone a little bit of a head start.
If you have an idea for a game but are unsure how to do something, let me know. It's probably easier than you think. Like changing the text in a NES game is usually as easy as editing a regular text file once you're set up.