First I'd like to explain the project:
I am creating a single player episode and I have a lot of plans in store for it.
There are a few things I want to implement.
There will be a couple of new weapons in the game. Balanced weapons of course. The first will be a hand held shotgun. It is rather primitive and will be found early. It will have a wide spread with a little more pellets than in the standard shotgun, but the pellet damage will be significantly lower. Also the reload time will be the same of that of the super shotgun.
The second new weapon will be a plasma pistol using cells. Damage will be lower by a couple points to the rifle as well as the firing rate will be that of the regular pistol.
There will be new powerups. A yellow armor that will give 50 armor, and a red armor that will give 300 armor. There will be others as well.
I will also be using monsters from the Beastiary monster assortment. I will modify some of these monsters slightly to balance them with my maps. I will also create some of my own. I will create "mini-bosses" which will be faster and stronger versions of other monsters. It will be necessary to kill them because they will drops keys, open doors to secret passages and so on.
The maps will give the player significant challenges. Such challenges are puzzle solving, ammo conservation and using the environment to their advantage. Instead of pitting the player against hundreds of enemies, instead the player will have to play smart against fewer enemies. Cannon fodding will only lead to failure. There will be points where ammo is scarce and will have to rely on ammo dropped secret passages with ammo caches, and using the environment to kill enemies.
I just fleshed this out in the past couple of days.