All - here are some suggestions. Years of combined play experience with a couple of newbies. A couple of us are also Army veterans with hand-to-hand experience. The purpose of these suggestions are both to simplify rules and clarify definitions.
Charisma as save vs Charm. As quoted from the rules Charisma represents "...the strength of your personality. A high Charisma suggests a strong sense of purpose...". By definition, it seems like Charisma is a perfect counter to Charm spells. It also makes Charisma more attractive as an Ability Score, and maybe even allows it back as a bonus for elves instead of total resistance to charm.
Perception - This is a biggie. Perception as its own Ability Score and would represent alertness. Checks would be for spotting a hidden creature, listen for noises. Wisdom is more of an attunement to empathy and would still be used for discerning mood, or sensing motive. This allows a player to create a vigilant, veteran soldier. Right now, with current rules, the cleric is the most alert on watch instead of the fighters.
Actions in Combat
Disarm, Grapple, Knock Down - You make a successful Str or Dex check (your choice) against a creature's Str or Dex (their choice). This allows creation of nimble fighters; more like Aikido or Judo versus brutes.
Grapple - If you succeed, the creature becomes Restrained. Since "Restrained" is already defined as a condition, it makes it easier to explain. It also makes unarmed fights more dynamic and fluid.
Moving a Grappled Creature - You can drag, carry or push the creature. A small clarification that made it clear that you could restrain a prisoner and lead them ahead of you.
Pinning a Creature - Thought about changing this to Knock Prone a Creature, since again Knock Prone is already a defined condition and gives more of a brawling or pancration feel.
What happened to "roll for crit" on a natural 20? Does this mean if you can only hit a creature on a 20, it will always be a crit? I'm still on the fence on this one. It does make for fun gaming when you see that "20" come up and everyone cheers.
Two-Weapon Fighting - If both weapons are light, only one of them gets the -2 penalty. The other gets no penalty. Just a clarification.
Corrosive instead of Acid - Broader definition that includes acids, bases, etc.
Crushing instead of Bludgeoning - Again, broader definition that makes constrictions and falling rocks easier to include.
Magical Force instead of just Force - Easier to show the difference in magical, kinetic attacks versus a fist-slam.
Thunder might be better as Concussive
Suffocation - An effect that cuts off the ability to breathe. Could allow for easier rules on drowning, head chokes, buried in sand, gas clouds, etc.
Exposure - Could allow for rules on starving, thirst, desert treks, etc.
Damage and Dying
OK, another big one. There's a great chance to fix the whole "bloodied" thing and give an epic feel to fighting as a hero/villain. Since hit points are already defined as an abstract - with luck, dodging, holy favor, bravado all as factors - here's what I'm suggesting:
1 HP or better - You are on your feet and fighting. Minor scratches, bruises or just a bit fatigued.
0 HP or lower - This is bloodied. You are hit hard and knocked prone! Now you are in trouble. But not unconcious! You can get up as the regular rules for standing up from prone. If you manage to get up you cannot attack or use Full Defense, but you still get your normal AC bonus. Your movement is 5 feet or 10 feet if someone assists you. Most creatures at 0 Hp or lower just die. Many villains may try to negotiate or give up at this point. This represents broken ribs, mortal wounds, etc. You can manage Long Rests and even sit on watch, but you remain restricted in movements and attacks until you are healed to 1 HP or better. You cannot carry more than your Encumbered weight.
Dying - You are unconcious and dying when your hit points drop to a negative number equal to your Con plus level. Now you must make the Death Saves to stabilize. You may make a Death Save once per round. Three failed Death Saves and you are dead (AKA the 3-count). Making a Death Save means you are Stabilized. But you are unconcious and will not recover until you are brought back to 1 HP.
Currently, dwarves and elves raise their damage on a racial favored weapon by one die type. This one is hard to explain to a new player. Especially when you just spent 10 minutes showing the difference between an 8-sided die, a 10-sided die, and a 10-sided percentile die. It's also hard to remember why one person with an axe is doing 1d8 but the dwarf had 1d10 or whatever. I suggest two things: make it a flat +1 to hit/damage. Also, the weapon HAS to say "Dwarven" or "Elven" in the description. Then you don't have to limit it to just hammers and axes for dwarves and bows/swords for elves. It has to be a "Dwarven hammer" for a dwarf to get the +1. To anyone else, it's just a well made hammer. But then you could have "Dwarven dagger", "Dwarven sling", etc.
That's all for now. I know I'm stepping on some big things here, and some will say to just "House Rule" it. But these are things that I've found helpful and wanted to share as an opportunity to improve our game.