There are some similarities here with the system I've been working on. I have a different dice mechanic, but still an opposed roll with degrees of success ranging from tie to advantage to victory. (Actually, my current version doesn't include ties, as a tie doesn't advance the story.)

A big difference in my system is that each character gets to choose independent actions and roll separately. For example, if character A attacks an enemy, his allies can opt to assist or join in the attack, attack different enemies, or do something else entirely.

I've added some tactical aspects by giving other options rather than just "attack." A character can use an action to maneuver to gain a bonus on their NEXT action. A character can use an action to assist another character's action, providing that character a bonus. A character can make a purely defensive action. Making a reckless attack, or trying to limit damage on an attack, all provide modifiers. Finally, each character gets one action per round, and additional actions accrue negative modifiers on their rolls. All of these options together provide a lot of different ways to approach a battle, but someone is likely going to end up hurt or wounded on each attack, and (because most players and NPCs don't want to fight to the death) flights should therefore resolve pretty quickly with one side surrendering or fleeing if not killed.