DND_Reborn
The High Aldwin
First, I don't like long posts--so I apologize for the length of this one... Also, as usual, this is not for most and I am ok with that. 
I've mentioned this idea here and there in other threads, but I wanted a place to put it out there on its own. In the (relatively) near future I will be running our game as DM for a while. Being the rule-tweaker that I am, there are several ideas I will be implementing but this is the most important one:
Everything has half its listed hit points.
Well, okay, not quite for PCs, who are closer to 53-55%, but otherwise it is universal.
An orc? HP = 15 right? Not now, it is only 7 (I round down).
An ogre? HP = 59 is now only 29.
An adult red dragon? HP = 256, but will only be 128.
And so on...
For PCs it is slightly different. You begin with max HP and your hit point modifier (discussed later). At 2nd level, you get only your hit die and then at 3rd level you get only your hit point modifier. This repeats so on even levels you get a hit die, and on odd levels you hit your hit point modifier. This results in slightly better than half normal hit points, but not by a lot.
So, why am I doing this? BECAUSE COMBAT TAKES WAY TOO LONG! The culprit? Hit point bloat (IMO anyway).
It also has some great side-effects!
1. It really makes low CR creatures more potent because not only can they hit, but when they do it matters MORE. Think about it. A CR 1/2 Goblin can hit a AC 20 with 16 or higher (25%), which is great and part of what bounded accuracy was supposed to do. For a PC with 50 hit points or so (say about 5-6th level), those 5 points of damage aren't a big deal really. However, with my idea the HP would be about 30, making 5 points much more significant!
Now, I realize if the goblin has its normal hp, it might survive a second round and get to attack again, maybe hitting for 5 points. So the idea with the bloated hp is it keeps combat going a long time because things survive long enough to keep hitting repeatedly and wear down the PCs. But that is the problem... a slow beating down of the PCs and combat dragging on and on.
2. Scary monsters are SCARY, I mean like WOW, SCARY! So, an ogre does 13 damage. Pretty nice, right? Sure, with 50 hp that is about 25%. But, with only 30 hp, it is 43%! Makes that ogre a bit scarier, huh? I think so. Of course, with only 29 hit points, the PCs will kill the ogre more quickly, but again that is the point--to speed up combat.
3. Magic kills. Sleep can actually affect things. In 1E, the average ogre (4d8+1) had 19 hit points. Sleep actually had a 50/50 chance of working. In 5E, it won't work until you get the ogre down 30 hp or more typically. Well, people might cry out "NO way! Casters would be too powerful!" accept they aren't since they will also have fewer hit points and be just as vulnerable to enemy casters as their opponents are to them.
I could go on, but I am shaking from how long this post is already so one final thing:
The Hit Point Modifier.
Forget CON. Lame. Because CON is tied into hp, for most characters it is the 3rd or better stat, rarely 4th, and super rare for 5th or 6th. With the "abstract" idea of hp in 5E being more embraced, I have gone further....
Your Hit Point Modifier is equal to the modifier you have for your highest ability score. This means a wizard will gain his hp bonus from INT (most likely), a rogue from DEX, etc. Now, we use CON in other ways so it is still important to the game... but that is for another post.

I've mentioned this idea here and there in other threads, but I wanted a place to put it out there on its own. In the (relatively) near future I will be running our game as DM for a while. Being the rule-tweaker that I am, there are several ideas I will be implementing but this is the most important one:
Everything has half its listed hit points.
Well, okay, not quite for PCs, who are closer to 53-55%, but otherwise it is universal.
An orc? HP = 15 right? Not now, it is only 7 (I round down).
An ogre? HP = 59 is now only 29.
An adult red dragon? HP = 256, but will only be 128.
And so on...
For PCs it is slightly different. You begin with max HP and your hit point modifier (discussed later). At 2nd level, you get only your hit die and then at 3rd level you get only your hit point modifier. This repeats so on even levels you get a hit die, and on odd levels you hit your hit point modifier. This results in slightly better than half normal hit points, but not by a lot.
So, why am I doing this? BECAUSE COMBAT TAKES WAY TOO LONG! The culprit? Hit point bloat (IMO anyway).
It also has some great side-effects!
1. It really makes low CR creatures more potent because not only can they hit, but when they do it matters MORE. Think about it. A CR 1/2 Goblin can hit a AC 20 with 16 or higher (25%), which is great and part of what bounded accuracy was supposed to do. For a PC with 50 hit points or so (say about 5-6th level), those 5 points of damage aren't a big deal really. However, with my idea the HP would be about 30, making 5 points much more significant!
Now, I realize if the goblin has its normal hp, it might survive a second round and get to attack again, maybe hitting for 5 points. So the idea with the bloated hp is it keeps combat going a long time because things survive long enough to keep hitting repeatedly and wear down the PCs. But that is the problem... a slow beating down of the PCs and combat dragging on and on.
2. Scary monsters are SCARY, I mean like WOW, SCARY! So, an ogre does 13 damage. Pretty nice, right? Sure, with 50 hp that is about 25%. But, with only 30 hp, it is 43%! Makes that ogre a bit scarier, huh? I think so. Of course, with only 29 hit points, the PCs will kill the ogre more quickly, but again that is the point--to speed up combat.
3. Magic kills. Sleep can actually affect things. In 1E, the average ogre (4d8+1) had 19 hit points. Sleep actually had a 50/50 chance of working. In 5E, it won't work until you get the ogre down 30 hp or more typically. Well, people might cry out "NO way! Casters would be too powerful!" accept they aren't since they will also have fewer hit points and be just as vulnerable to enemy casters as their opponents are to them.
I could go on, but I am shaking from how long this post is already so one final thing:
The Hit Point Modifier.
Forget CON. Lame. Because CON is tied into hp, for most characters it is the 3rd or better stat, rarely 4th, and super rare for 5th or 6th. With the "abstract" idea of hp in 5E being more embraced, I have gone further....
Your Hit Point Modifier is equal to the modifier you have for your highest ability score. This means a wizard will gain his hp bonus from INT (most likely), a rogue from DEX, etc. Now, we use CON in other ways so it is still important to the game... but that is for another post.