It's basically a 3rd person medieval warfare fighting game that has its setting ripped from our world via some obscure cataclysm that has pitted Vikings, Samurai and Knights in a perpetual war over resources lasting hundreds of years. I have no idea if there is an actual campaign, but that is the justification for the setting. I don't think they were trying too hard to be serious with it lol. They just wanted an excuse for Knights, Vikings and Samurai to fight one another.
The combat changes depending on the game type. Fundamentally it is a third person action/fighting game set on something akin to FPS maps. However it can be straight up duels, elimination or domination. The first two types have no mobs and are entirely player vs player. Domination has waves of mobs from both sides vying for control of the map while the heroes (players) try to sway the tide of battle and capture control points. There is a good deal of item customization and loot. The closest comparison I can think of would be the recent Call of Duty games and how you unlock pieces of armor, weapon parts and so on and so forth.
The game is fairly fluid and feels nice. Combat is weighty and there seems to be a decent skill ceiling. I'm usually pretty good at PvP games from the get go and I'm getting stomped by many people lol. Then again, there are plenty of bad players too so new players will not be out of place at all.
I'd link some YouTube vids but I'm on mobile. Check some gameplay videos off of YouTube though. Pretty neat game.