If your turn doesn't give you enough movement to run up to the enemies and stab them, you can't say "I run next to the doorway and wait to stab the first person who runs through it."
Instead, you have to waste your turn and then stand around getting attacked. So it's often to your advantage to roll worse in the initiative order, because the enemies will spend their turn dashing to within your movement range and then you actually get to hit them on your turn. Kind of hate it, rolling high initiative is supposed to let you get the drop on people or set up the battlefield more to your liking.
BG3 players, please let me know if I'm missing something here.
And either way, if there's a crowd of archers in the next room I wouldn't want to walk in (sneaking or no) where I have no cover, so I'm going to try and hold at the door. Still the better play even if it costs a whole turn of not being able to use my action.
The missing Ready action really tilts things toward those "alpha strike" characters made to hit first and hit hard, which isn't a design choice I like much. I want to be able to lure enemies into a room with minor illusion or other sounds and have the whole party readied the jump them.
The ready action is designed to get used for delaying actions to bypass initiative order.
As far as readying an action, at minimum it could work like XCOM's "Overwatch" action, targeting the first enemy you see within range.
But it would be nice to give you a choice of targeting options so that you can designate a smaller area, just in case that's useful. But fine leave it as "first enemy in this area" instead of trying to give you full pencil and paper D&D flexibility. There is a UI for picking between options in an action, such as Enhance Ability needing you to pick an ability.
Speaking of delay, I know that's not part of 5e (it was in 3.5), but if we can't have ready action could we at least have the delay option? A lot simpler to implement and it'd at least help with the situations where you would have been better off at worse initiative.
The way readying usually works is basically "move + guard", though it's more flexible than that in regular D&D with a human DM where you can line up whatever action you want like "I'll stay put, but if the goblin comes toward me I retreat into the next room" rather than only being for attacks.
But if they wanted to only implement it as letting you attack or cast a spell when an enemy enters a target area, that would be a lot better than nothing.