Originally Posted by GM4Him
One thing that might be a good compromise that I've always wanted someone to do:

An RPG combat system where players pick their moves and targets, and then the combat plays out a full round before your eyes, all combatants moving simultaneously.

So, how that would work is, I select my main, pick attack Goblin Captain. I then pick Use Shield of Faith as my bonus action. I pick Gale and select Magic Missile and pick Goblin Shaman as target. I pick Lae'zel and select attack Goblin Berserker. I have her use Action Surge and pick Berserker again. I pick Shadowheart, choose attack Shaman and Shield of Faith. I lock in decisions and the round plays out. If an enemy is killed before all actions used, game pauses and asks for me to pick another target. If enemy moves out of range, I again pick another target. Something like that. After all actions for the round are used up, game pauses again for the next round selections. As far as who might hit who first, the higher initiative wins.

So it is still turn based but everyone moves simultaneously each round and yoy never know what your enemies are gonna do. Kinda like Xwing Tabletop by Fantasy Flights.
Depending on who you ask (see page 87 of this thread), this is how D&D 2e combat works. Everyone declares their intended actions, then initiative is rolled, then the actions occur. If you were planning on shooting an arrow at a goblin who died before your turn, well, congrats! Now you shoot an arrow at the dead goblin, or it dies while your arrow is in mid flight. I played a 2e game that way and it was fun, though honestly rolling initiative every turn and dealing with weapon speeds was a pain. Of course, these problems are all solved by letting the computer do the work for you!

I think your suggestion of "if an enemy is killed before all actions used, game pauses and asks for me to pick another target" would be more user-friendly but honestly would take out a lot of the fun/tactics of such a system. Such a system is supposed to embody the chaos of battle, where sometimes you go to do something but it's rendered irrelevant by the time you get there. This suggestion would move it much closer to the standard RtwP, although this is not necessarily bad...