Because I was led to this thread with an overhyped title, and it massively under-delivered, this will most likely be quite snarky.
1) Hit Die (Hit Points)
I don’t like the current system at ALL. Rolling for hit points is SO CRITICAL, people get angry and then as a GM you let them re-roll anyway. SO having a mechanic like this broken imho. Also, has many others have stated the con modifier to the minimum really favors people rolling D4 or D6 over the fighter rolling d10.
So, here is the fix. Your Constitution modifier adds to the number of die you roll taking the highest roll (minimum of 1 die rolled). So my Wizard with a Constitution of 12 (+1) would roll 2d4 taking the highest roll. My Fighter with a 16 Constitution would roll 4d10 taking the highest one. I think this is a great compromise and makes Constitution more useful and players would feel better about the rolling and keep the same “spirit” of what you are trying to do.
Or, you could just have a module for fixed style/for those that love rolling. Con does need to factor into them in a meaningful way (more than Next). No reason to re-invent the wheel when there are only two choices people want. Roll if you want luck. Don't if you don't.
2) Health and Healing:
There needs to be a new system. I personally like Wounds and Vitality (you can still call them Hit points) Wounds equal your Constitution and heal either by magic (healing spells would need new math) or natural healing of 1 per day. Hit Points (Vitality) represent combat endurance and heal to full after a short rest.
Once you run out of Hit Points, you start taking Wound damage. This would increased survivability, maked Constitution a more valuable stat, and it's a pretty good compromise.
Really? HP is a very broad system, representing a variety of factors in combat (luck, morale, energy, actual damage). I can't imagine WotC changing something that has actually worked for each edition just because you like something more complicated.
HP + reworked surges = simple and easy.
3) Critical Hits
I personally like max damage, because rolling 4 on a critical hit roll sucks! However, if you implement #1 Critical hits can still be max damage or an option rule would place a critical hit as normal damage directly to WOUNDS… OUCH!
My favorite option would be Max damage + weapon die roll (since we roll hit die and damage die at same time). It just depends on how deadly you want combat to be.
Critical hits aren't that even that big of a deal, and your wound system is bad.
4) Spell casting.
Well this is a tough one. I personally really like what they have done with the mix of at-wills and resource casting. I really think it’s hard to tell how it will really play out until we can test level 5 – 10. However, at 3rd level 4e you have at-wills, 2 encounter, 1 utility, & 1 daily: In 5e you have at-wills and 6 dailies, so you max in 5e is 3 encounters before you are empty and in 4E you would still have 2 encounter powers.
I’m really on the fence on this topic, BUT I would increase the casting to:
1st Level: 4
2nd level: 5
3rd Level: 5 and 3
Not even sure what it is you are suggesting. Tweaking the amount of spells they get I think? What a radical change that will interest all camps involved.
I don’t get the uproar over Heavy as much as some people. Most of my fighter/tank have never had more than 12 Dexterity so Plate Mail is always better than Medium armor. However, I think it is time the reworked the armor.. so here goes:
Armor & Shields
Light: + Full Dexterity
Leather: AC 11
Studded Leather: AC 12
Chain Shirt: AC 13
Mithril Chain: AC 14
Medium + 1/2 Dexterity
Ringmail: AC 13
Scale: AC 14
Splint: AC 15
Dragon Scale: AC 16
Heavy + 0 Dexterity
Chainmail: AC 16
Banded: AC 17
Plate: AC 18
Adamantine: AC 19
Light: AC +1 (No penalty)
Heavy: AC +3 (Eliminates any Dexterity bonus to your AC)
Your "rework" is tiny tweaks to the AC value. Count me not blown away.
6) Dexterity the Super stat
Ok, so this is RADICAL! We have always done it this way needs to change on this topic. So, here goes. Remove damage bonus from Dexterity from Finesses weapons and use Strength (like it was in 3e). Use Wisdom as your initiative modifier. WHAT?!?
I know crazy… here’s why; sometimes game balance has to take precedence over realism. Also, Wisdom is perception so I could argue that if I can’t perceive anything I can’t reacted to it. I could be the fastest gun in the west but if I’m shot in the back playing cards all that speed doesn’t help me.
Cool, annoying complicated weapons that use different stats for attack and damage. Make other stats more important. Tough sell on changing Init from Dex to Wis. Being perceptive usually amounted to Suprise Round, not flat out reflexes. Dex is amazing now because the bare bones rules haven't provided any additional information on the other ones.
7) Charisma the dump stat.
But Charisma does so much! Well, not really. So, how can we fix it. I LOVE action points. This makes NO LOGICAL sense from a reality stand point, but again game balance. Use the Charisma modifier as you action point value. 0 – 13 = 1 action point, 14 – 15 = 2, etc.
I'd like to applaud you for actually posting something actually meaningful. But again, we need to see a more expanded stat system before I'd advise any radical additions.
8) AoO and movement
I like the feel of the free movement. However, having orcs run by 4 characters to kill the wizard in the back isn’t fun or add to game balance. Yes the Guardian theme can stop ONE person, so 3 go by…still not fun.
There have been suggestions about giving disadvantage to people disengaging or moving through threaten areas (squares). I don’t like this because I think it will just mean people will go for the crazy super action since they can only get one disadvantage penalty (they don’t stack). Another solution could be a disengage roll. However, that adds more rolls.
I would simply say if you have been hit in melee combat on that round you cannot disengage unless you take a FULL ROUND action (hustle action) directly AWAY from the combatant. So, no additional rolls, and anyone can block by Readying an Action and if they hit it stops movement.
9) Surprise Round (removed after further discussion)
That’s all for now.
The perils of grid-less combat. It's like playing cops and robbers as kids, except the cop decides if and when any of the attacks hit. You are trying to put a penalty into provoking AoO without actually provoking an AoO. Again, if why re-invent the wheel? If you don't want 4 orcs running around, use AoO. It's not that hard of a mechanic.
Your fixes are tiny or irrelevant tweeks to an initial playtest that fail to address the main issues between the two primary camps. Next time don't try to sell your "fixes" so hard with your "30 years of experience". "My personal views to the initial playtest" would have been suffice, because I came in here expecting actual game design, and was rewarded with a bunch of completely bias and unfounded changes, with little to no explanation WHY these changes were needed.
In case you cant tell, it REALLY irks me when people open their arguments with their amazing commitment to the game, as if it is provable in any way to the people they are talking to and somehow gives their personal views of the game more credence than the next poster. It's the internet. It doesn't.