In "Mirror's Edge" there is a simple and effective gameplay mechanic I really like.
If you pick up a weapon, you have:
After you run out of ammo and you don't know when, the gun is automatically discarded.
Although the weapon mechanics in the game feel cumbersome and not refined the idea behind its implementation is effective.
I love the simplicity of it.
If I were to design a game, I would try to implement this mechanic. I wouldn’t make the weapon discard automatically after you run out of ammo. That should be up to the player.
I would also add a way to take out the magazine to check how many bullets the gun has left. So as you play you would have to check how much ammo you have or count the rounds as you shoot.
Speaking of "Mirror's Edge", I have a tutorial for "How to Use Color to Create Environments Like Mirror's Edge" on WoLD.
I wrote a book on how to plan your level designs and game environment art. Buy the book in PDF, Paperback or Kindle version.