In the original Fallen Earth melee weapons were pretty much silly and under-powered due to their limited range. Increase the amount of Melee Weapons available and their usage.
I suggest to create a system that grants up to 3 random attribute/effect/trigger bonus to every Equipment or Accessory. This is to increase economy and diversity among players -- and why not, offer more build opportunities.
Ranged Damage vs Melee. No one would think twice, everyone skips to Ranged immediately. Fine, at least introduce some "Sprinting" ability that allows Melee Weapon Wielders to gap closer with Ranged Enemies before dying...
Give meaningful ways to increase character's resilience, resistance vs damage, and avoidance. The original game was kind of "let's go and kill", I'm pretty sure no one cared much for turtling because it was lackluster and useless.
Remember to balance the game for meta, and do not create any situation in which (x) damage reduction is ignored. That's how games whose battle component is made of RPG mechanics go unbalanced.
The game is old, thus it requires REWORKED CHARACTER ANIMATIONS, WEAPON ATTACK ANIMATIONS, ABILITIES CAST ANIMATION -- most of them look and perform slow and terrible.