I think 5e’s action economy works fine, but is more confusing than it needs to be because of its insistence on trying to pretend it doesn’t have one. How it actually works is you have three types of actions: one standardaction, one minorbonus action, and one swift actionobject interaction. Additionally, you have one reaction and an amount of a resource called movement equal to your Speed that you can spend to move your character, as well as to do other things like mounting creatures and standing up from Prone. Unfortunately, all of this is obfuscated by the game’s language.
The name “bonus action” is confusing because the natural assumption when you have multiple abilities that say “you can use a bonus action to...” is that you can use them all, because they’re bonuses to what you could otherwise do. But no, you only get to use up to one bonus action on your turn, and allegedly “you don’t have a bonus action to spend” unless you have an ability that lets you do something as a bonus action. This would be so much more intuitive if they were called minor actions and the game didn’t try to act like they don’t exist until they have to.
Object interactions are weird because it’s unclear when interacting with an object counts as this and when it requires the Use an Object action. Saying that you take them “as part of your action” or “as part of your movement” is also unnecessarily confusing and seemingly done only to try and maintain the illusion that they aren’t an independent type of action.
Reactions and movement I think are great. Making movement a more granular resource rather than a single “move action” is a cool piece of design tech that allows for interesting things like breaking up your movement with your attack, and movement as a cost for things like mounting and standing up. I think this is a bit under-utilized; for example, I feel like you could make the old “shift” a thing you can do by spending movement equal to your speed instead of making Disengaging an action. Reactions aren’t as innovative as movement, but they are still solid design; they’re clear and they work well.
And then there’s Extra Attack, and things that cost one of your attacks to do... This is probably the aspect of 5e’s action economy I like the least. You just have to memorize what things only cost one attack instead of a whole action. And it’s only relevant for martial characters of 5th level or higher. Ick.
EDIT: Oh, and the part where if you cast a spell as a bonus action you can’t cast a spell as an action unless it’s a cantrip. That’s a pretty awful rule.