I'm working on a classic Adventure Game for the game jam. It's my first real game, although I have experience with making maps for all different kinds of 2D and 3D games.
The first step was laying out the story, locations and puzzles.
Then the making of the rooms began.
I'm using Paint.NET to create them, painting with a mouse.
The very first room created was the outside area of the Smoke Box.
Inspired by old concept art from Day Of The Tentacle, I started by sketching 2D outlines.
I then colored over them and added shading in a second pass.
This was the first lesson. I should not do that again.Adding shading, textures or changes was hugely time consuming. I constantly had to stay within the zone of the area I was pimping up.
This was the first and last room I created with this approach.
The good news: I have tons of room for imperfections and mistakes, because the final background will be downscaled to an old-school resolution.
The next room was the interior ground floor.
I now eliminated the sketch outline approach and instead started to create every object individually on its own layer.
This makes the image project a bit more complex, with hundreds of layers existing at times.
(I label each layer to keep order, and combine layers once an object seems "sound".)
The great advantage: I can now make changes quickly and easily to any desired part of a room.
Put a gradient on the back wall? 30 seconds. Make the backroom darker? 60 seconds. Change the color of the counter? Just select its layer and shift the hue!
Now all rooms are done, at a core functional level, even if I would like to add some rough spotlight shading and little details, like dirt on the floor or cracks in the walls.
I postpone those tweaks, as the creation of the game part had to finally begin.
I'm using the open source software "Adventure Game Studio" which is rather straight forward and simple to use.
But the clock is ticking. I don't assume to have the game finished by the end of the countdown, but hopefully for Bosman's streams of the submissions. I already cut down a lot to accelerate the process, but the main problem isn't over-ambition, but lack of time.
The game will be pretty easy and straight-forward, and a playthrough should stay below the 30 minute mark at any skill level.
My progress depends on the amount of hours and energy that I have left to work on this game after coming home from work.
The animations will be very simple (walking and a general "interact" hand movement) and there will only be two characters to animate. Some inventory items have to still be designed (for both their depiction in the world and the inventory), but these are only a few, easy-to-draw objects (like a balloon or or plunger). I would like to make some music at the end, but depending on the time I have left, I'll maybe just make some simple and short midi-quality loops.
I don't know when I will post another update, as creating this post (and the images/gifs) was an hour that I could have worked on the game itself - which is why I haven't done any post so far. But I wanted to share the rooms I've made, now that they are all finished at a core level, with only rough lighting and interactive objects missing.
I also think about artificially reducing the colors (on a scene-by-scene basis) and creating some dithering in the process, to add a little touch of retro Sierra-Style grime. 
EDIT:
Removed images of other rooms to avoid showing too much.