I don't know if I could just stick to one idea/game. I've been having so many thoughts rushing through my head about improving existing games and even creating new ones, but I always see myself coming back to horror. The way I envision these games in my head, I know they'll work, but not for business. That's what's wrong with this industry today. Great ideas won't work unless they appeal to the common simpleton. With that said, if we lived in a perfect world where I can be in charge of the creation of a video game and have the budget to make it as great as it is conceptually, then I would craft multiple survival horror experiences all with varying themes and play styles.
Inspiration for my ideas mostly come from my own fascination and psyche, but also some of my favorite entertainment. So for my first idea (which I'm coming up with for the first time as I type), I was thinking of doing a mystery encounter with aliens that doesn't rely on senseless action. For this particular game, I want to focus on story and mystery. It'll take place in a small town, farm and fields, government facility, and inevitably take you on a space ship... or new world. I want these aliens to be ferocious, fast, vengeful, stalking, and controlling, in turn, making the main character very vulnerable.
The idea may sound generic, but I really want this to be a study of humanity that deals with themes like ingenuity vs biological superiority, human cruelty, precaution of the unknown, etc. Which will be reflective in the gameplay by not arming you with everything and leaving the most convenient items lying around, like ammo cases and an array of guns. I want the player to use their ingenuity to take out their targets. I want practical things that you would find in these environments. The enemies are also more than just a plot device, there's a history, reason, and motivation to all this which will remain a mystery for most of the game along with other plot points that eventually intertwine.
I think my ideal developer for this game is Remedy. Alan Wake has inspired a lot of my thoughts for some time now, including this one, which really makes them the obvious choice. They've done such an amazing job with atmosphere, writing, and story telling before, so it's a no-brainer here.
I've also had a more ambitious idea for an open world horror game for a while that I don't really feel like diving into right now. There's been so much going on with that idea ever since I first came up with it a few years ago. It's just constantly evolving.