I've posted a few Highlander related game wishes throughout the years on this thread, so here's another one: Just a straight up Battle Royale.
The main crux of the game would be that the ONLY thing that can kill a player is decapitation, which can only come from other players. There'll be the usual duels, using whatever the most feasible and accessible sword fighting system there is in games these days. The goal in all these fights is to inflict enough damage to break your opponent immortal's posture, stunning them long enough to do a decapitation.
Now, of course a lot of other things can HURT the players, such as fall damage, fire, environmental hazards, and if a player is caught and isn't able to heal fast enough before another player gets to their prone body, they can get decapitated without a fight. But a player's game can only end by decapitation.
Every player starts off the match with I suppose you could call it a Heat Move, a special sword attack that does extra damage and nearly beats someone's posture down immediately, if it's landed with the right timing. Upon killing another immortal, the player who wins absorbs their opponents Heat Move, with all the Highlander Quickening lightshow accompanying it.
So a player that successfully hunts and defeats other players gets multiple Heat Moves, which can be represented by differing sword techniques from different styles. The more opponents you defeat, the more Heat Moves at your disposal ( they'll probably have a very long recharge time ) for the final confrontation.
This allows for two play styles. Hunt other immortals and have an arsenal of heat moves so that the final battle is a bit easier, or if you're more confident in your mastery of the basics you can run and hide, and in the final battle use conventional sword attacks and environmental trip ups to secure a victory.
The map could be a modern day city, the Scottish Highlands, Rome, a Japanese city, Medieval Europe, 18th century America, etc. And apart from other players in the battle royale, who would of course be other sword wielding immortals, there'd be tons of NPC opponents and obstacles. Police in the modern day, Scottish highlanders, Roman soldiers, that kind of thing. They'd be using weapons like guns, spears, bows, and stuff that bypass posture, and can stun you, but they can't decapitate you.
They're not that difficult to kill one on one, but there'll be a lot of them, and they can hurt you and bog you down enough to give another Immortal a chance to finish you off.
Every few minutes, you get an alert for the direction of the nearest immortal to you, and when it's just the last 2, that's when the map starts closing in.