The complexity would be depth of choices or less abstraction. So you would have different materials for armor, weapons, spells, more classes versus subclasses, or an equivalent of maneuvers for all martial classes to provide the same flexibility as spells. In regards to tactical depth I do not mind more static modifiers versus advantage/disadvantage. I did not like the craziness of 3E and any motion provoking an AOO, but 5E went too far to simplify it.
I love to tweak things, but as I've tried to add complexity to the system I'm finding that things are extremely well covered in the rules. With some additions and minor modifications it's easy to do. And I guess that's one reason why I love this ruleset so much, it's extremely easy to modify:
Grapple
Opposed STR check: Both are Grappled
Disadvantage on grapple check to use bonus action to:
Attack: with light weapon
Cast Spell
Choke DEX save or suffocating
Disarm/Grab defender has advantage if using both hands
Draw a Light Weapon
Move: ½ speed and drag opponent(s); full speed if target >= 2 sizes smaller
Pin/Restrain: both are restrained
Tackle: both are knocked prone
Throw: knock prone 5’ in any direction
Use Object or Item
and
Special Maneuvers
Attack with disadvantage
Impose condition until your next turn
Saving throw DC 8 + Attack modifier
Disarm/Grab: DEX save or drop item
Garrotte: DEX save or suffocating
Groin, Sap: CON save or incapacitated
Eyes: DEX save or blinded
Lasso, Net, Pull cloak/sack over head, Staple: DEX save or restrained
Sunder: DEX save or damage item
Trick Shot (Archery): See similar effects
Trip: DEX save or knocked prone
These are all based on existing mechanics and just add some options and color to the game. Part of why I've spelled them out in my campaign is to get away from the 'attack to kill everything' approach. Now the players have options that they might not have thought of. And I use them against the PCs too, which highlights their usefulness.
When the 2.5, 3, and 2.5 progression was happening, we dove right in and loved it. But I know that there were always circumstantial modifiers and such that we forgot to apply. With the 5th edition you can always add an in-between modifier:
If you have an edge in the circumstance, but not quite advantage, you get a +2 bonus. If you have been outsmarted, but not to the point where you have disadvantage, you have a -2 penalty.
Any other tweaking I've done is to fit the rules to my version of the Forgotten Realms. The vast majority (like disease, injuries, and poison, along with the ones presented above) are specifically to be able to model with the rules the actions and scenarios that I think are important to the story and story-telling nature of the game.
I have injuries because there's always somebody (even in the first two published adventures) who is too hurt to be able to help the party, or the king is at death's door due to disease or poison, etc. Nothing explains why nobody has bothered to come by with a 2nd level spell to fix the problem. My answer is that it's not a 2nd level spell problem, it's a 5th or 7th level spell problem and they are much harder to come by. The fact that you can cure a disease or neutralize poison, but not exhaustion at 2nd level doesn't make sense.
Hence a disease, injury and poison system that leverages the exhaustion system (and requires multiple 5th level spells to heal). Why the (tweaked) exhaustion system? Because despite its abstractness, the basic effects (symptoms) work well regardless of what causes those symptoms. I require 3 death saves to recover, one save per long rest (day). It effectively models a disease that can take weeks to worsen, improve, worsen again, and might even cause death. Severe injuries (like broken bones) also take lots of time to recover from. These occur rarely, but can have a real and interesting impact.
But I think you'll find that the basic mechanics are very sound for making the game as complex as you'd like.
Ilbranteloth
