I've been running 5E on a consistent basis for several groups since it was officially released. Now that I'm basically leaving 5E, I'm looking at a few things that never quite worked for my groups and me.
...(issues)....
What did I miss?
Well, IMO you missed the opportunity to personalise the system for your table.
Besides the DM's Guild as well as Enworld and other forum sites which can be mined for a range of interesting ideas to incorporate into the game, the system is so malleable that it really allows you pull, twist and tease it into the type of game you wish to play.
For instance, the monsters are a bag of hit points comment always suprises me.
I can easily take a monster like an Ogre who is fairly uninteresting and turn it into something memorable by incorporating interesting mechanics just by using the ideas and inspirations from the core books.
(A) Incorporate Degrees of Success (DMG 242) into the creature's Attack, where every 5 or more on the hit roll adds a special effect in addition to the normal damage done.
Special Effect (1d6)
1-2. Disarm (DMG 271)
3-4. Shoving a Creature (PHB 195)
5-6. Sundering Armour/Weapon (DMG 246-247)
(B) Have the fluff mean something, so
Furious Tempers, allows them to Overrun or Shove Aside (DMG 272) as a bonus action. Allow
Greedy Collectors to play a part for smart PCs, so if in the middle of the combat, if a PC throws a handful of coin into the air, have the Ogre make a WIS save or be distracted, Incapacitated condition (PHB 290).
(C) Not all monsters have to fight to the death. The
Primitive Wanderers reflects that they like to
take advantage of poorly protected livestock, undefended larders and unwary farmers. This reflects a rather cowardly beast, if things turn dangerous for the ogre it will more than likely make a run for it, especially if it is outnumbered and if its attacks are proving ineffective. Their rage will only take them so far. Ogres look for easy game.
(D) Weather conditions, physical terrain all play a part in making encounters interesting and not a chore. Many DM's ignore this. Smart PCs can use the terrain to take advantage of this against these dumb brutes,
Legendary Stupidity luring them into narrow passageways to take advantage of Squeezing into a Smaller Space (PHB 192) or into makeshift traps to take advantage of tool proficiencies and skill checks (PHB Chapter 7).
(E) PCs do not necessarily need to use their combat prowess to defeat monsters. Too often DMs these days set safe encounters using the CR and encounter building rules so as to ensure character survivability instead of encouraging players to think outside the box to accomplishing their mission/s or to overcome difficult obstacles.
As a basic example - PCs want to retrieve an item stolen by a group of raiding ogres, they use their knowledge of these beasts,
Gruesome Gluttons, to lure them to a campfire where they have left copious amount of cooked food, with the ogres feasting on the "free food" the ogre den is now empty allowing the PCs safe passage to retrieve the item.
(F) Play your monsters naturally. Have them Interact with Objects Around them (PHB 190) while attacking, so let them rip the hood off a PC's cloak, break a branch from a nearby tree, smash a glass, overturn a table...just generally let them be the destructive-natured beasts they are creating interesting narratives.
Have them move in straight lines toward their targets, jumping over/on things, shoving things aside, trampling, lunging...
Combat is not supposed to be a slog and the fluff is there for a reason.