Grenades: They have normal and crit damage. Some allow a Fort save. This led to some confusion in game, but I think I take all that to mean that you still make an attack roll to see if hit, if a crit does the greater damage and then they roll a save as applicable. What do you roll for that, though? Agility? Once for all in the effective range and compare that to the targets' defense, presumably (to save on excessive rolls and bogging down combat). It's not seemingly Close Quarters or Firearms. Is that right or hits are automatic, it's just a roll to see if the damage is critical or not? The latter seems to make grenades a bit too powerful.
Actions in combat: It states you can move or attack, not both on a turn. I highly suggest allowing a move action and 1 other action. Spending a turn on just moving makes for extended combat and less fun.
Armor: It states that armor is depleted before dipping into health damage. That's all good, but does the armor absorb damage each turn or only until depleted? It seems like it needs to be the latter and you might state as much. This provides some balance and makes lesser enemies still a threat. Otherwise, many enemies can only do 1-2 damage and they are completely nullified. However, with health so low for starting PCs, I want to both make that the case and increase armor durability a bit in that case. I think reducing armor protection by 1 each hit (after calculating damage and your choice of armor if a shield is in play on top of worn armor) is the sweet spot for me. That way armor absorbs damage longer but still depletes and it makes you a little better against weaker opponents.
Starting and max HP: Even with the armor changes I want to make starting HP 6 and max HP 12 for a bit more survive-ability. I'm okay with death but quick, cheap ones are less fun. A bit higher allows a character to make more of an impact before lights out.
Anyway, those are my thoughts, suggestions after running a session.