A Fourth of July map by The Green Herring. It's a small techbase in some surrounding watery canyon, mostly themed like a "normal" Doom level except the textures are all recoloured in red, white, and blue. Even the three keys are red, white, and blue. However, it's not over-the-top with its gimmick, and all seems quite tasteful, especially the secret area with the painting in it. That said I think if I ever played with the game music on, it might seem a little more blatant.
The map itself is fairly disjoint with separate rooms to fight for each key. The monsters are numerous but so are the rockets (the only type of weapon you get). Lots of imps, revenants through a window, a room of cacodemons, more revenats, hellknights, and a finale involved even more revenants and a cyberdemon.
In summary The Fireworks Factory is a fun if not entirely serious little map, and certainly worth playing. I didn't find it particularly difficult, there's plenty of health and rockets. The main danger is blowing yourself up, with careless treatment of revenant missiles a second.