I was thinking 'I have a lot of puzzle game ideas, how about an FPS'? I'd like to make a Fun, simple FPS. I have memories of playing Goldeneye with my school friends in High School. The fantastic thing about Goldeneye is that ANYBODY can play it. We even had a guy who literally didn't know which way around to hold a controller and he could still play it!
Strangely though, all subsequent games made things more and more complex. Though this suits a person who likes to play FPS games, it tends to put casual gamers off the genre, which is a shame, because FPS games can be really fun to play with friends!
So let's go back to basics here.
My idea for an FPS is inspired by the water fights I used to have in the garden with my siblings. On a hot, sunny day, you'd get out the water pistols, super-soakers and even a bucket, and the aim was to soak each other. We even had this big plastic tray that could be used as a shield. Oh, and water balloons, which were a bit like grenades.
Water doesn't show up too well, so how about paint instead. Your aim is to cover the opposing player/team in as much of your colour of paint as you can. This is reminiscent of the 'paintball' mode in Goldeneye, exept that just put a coloured blob on whenever a character got hit, and the colour was random, not dependant on who hit.
The style would be bright and cartoony, maybe even Super-deformed, since a headshot would mean nothing in this game, it means big heads are no disadvantage. Bright, over-the-top, slightly chibified, cute characters might really work for a game like this.
To reload, you have to run to a reload point (just as we had to run for the tap). There are a few of these on a level. Some weapons have the advantage that they don't need reloading much, ususally the less powerful ones. You can see how much is in yours or a friend's weapon because the weapons are see-through and you can see the reservoir of paint inside. Paint-bombs are like grenades or bombs, and can be found around the level, they are thrown and cause a big splatter of paint, inaccurate but can cover a lot of people in paint if you're lucky! There's also the shield, which prevents the use of two-handed weapons or dual-wielding one handed ones, but shields the area it covers for a while, until it is covered in paint and must be discarded.
The controls would be very simple. Oh, and there would be other game modes than just 'soak the opposition' such as a mission where you have to tag certain points with paint, or capture the flag etc.
There are also 'water jets' in some places, which fire sporadically in a certain area and wash paint off. The player has to decide whether standing still, waiting for a jet is worthwhile, when standing still in an exposed area can be a dangerous tactic!
I think this sounds pretty fun personally.