It is extremely annoying to go into a fight that my entire party knows is going to happen, having a plan to initiate it, only for 3/4 characters to be "surprised" and miss a full turn, while enemies get a full free round never mind that my entire party passed their stealth rolls. On the whole, rolling initiative has been chaotic and unreliable, sometimes I get away with murder when I shouldn't, sometimes my party gets slaughtered when they shouldn't.
Sure, in a game of D&D it is possible for a party to be surprised by one player's actions, but more often than not we all know what we want to do as soon as combat goes loud. Having a system for players being ready vs. not ready might be ideal, but I think it would be better to err on the side of party members always being ready for combats that the party initiates. If my whole party sneaks up planning to attack an enemy and my rogue takes a shot, none of us should be surprised that the enemies respond, and we should all get a chance to take a shot or cast a spell as a readied action.
Readying an action is one of the more complex and dynamic mechanics of D&D, so a video game won't be able to handle everything a DM can, it might manage a good chunk of common triggers for a readied action to go off but it won't be perfect, but at the very least we should be able to get the start of combat.
A game that does this very well is XCOM: Chimera Squad, where all combats start with "breach mode", they add some special abilities and conditions that don't really fit D&D, but the main mechanic could certainly be adapted. In XCOM, when the squad starts the combat, enemies can be surprised, alert, or aggressive. Surprised enemies don't take any actions during the ambush, alert enemies take non-offensive actions, while aggressive enemies can use take shots. You could ignore the whole "alert" condition if you want, or use it to cast buff spells, take the dodge action, move to cover and things like that. Surprised enemies can have the surprised condition as expected, while aggressive enemies take actions as normal, moving and making attacks or casting spells including damaging spells. During this ambush round the party members get to take full turns.
Codifying the enemy response would let encounters play out in a way that is believable and balanceable. For example if we ambush a camp with a drunken guard and sleeping enemies, they are more likely to be caught by surprise, while if we are spotted by the enemy and they simply haven't decided whether to shoot us yet when we attack, they are much more likely to be aggressive.
Most of my frustrations with the game as it stands come from the unreliability of the beginning of combat, and it is definitely something that could be fixed.
