THIS GAME IS AWESOME!!!
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Additions:
Ammo Drops
New Maps
Multiplayer
Different Texture Packs
Level Editor
Progressively Harder Enemies
Death Screen
Health Drops
Rewards System
Flying Enemies
Grenade Launcher
Fall Damage
I think fall damage would ruin the aspect of jumping around, but I agree with everything out.
All except fall-damage, multiplayer (No way it wouldn't be laggy), and texture packs (we don't need them, and he could spend time on WAY more important stuff instead).