You could implement A cover system in with the lean, Taking cover behind a box, and do a TIP TOE. so you can look higher, and shoot over boxes, and bushes. You've got to have the Old school lean tho. So many games failed at using cover systems "Las Vegas 1 and 2". I thought you guys did a very good job on Ghost Recon 2, the cover system for that was VERY VERY UNFAIR, But you could have made it a great way to look over barriers in the level.
Another cool thing to add would be customizing you character, The more fat your player is the more health he can take, the more skinnier the more faster, and smaller- harder too get shot. Larger- Easier too kill, but have better vision. Something like that would make a new Idea to FPS.
Reticules!!! Need to make the game Perfect, MW1 Has a very GOOOOD GAMEPLAY/ ENGINE / PHYSICS, But Reticules FAIL so much. No sidestep, its all RUN AND JUMP. This is one of the most important things in FPS GAMES.
GAMEPLAY MAKES GAMES GREAT, NO MATTER HOW BAD THE GRAPHICS ARE - PacMan
Thank you, Cashingout