Call of Duty WW2 has a number of cool modes, but one in particular is held up by players as being especially awesome: Gun Game.
Here's how it works: Gun Game is a six-player free-for-all mode in which you are given a random weapon to use from a tier of weapons. Kill another player and you immediately get another random weapon from the next tier of weapons to use. The first player to get a kill with all 18 weapon tiers, or the player who used the most weapons when the time runs out, wins the game. It looks like this:
Gun Game is fast-paced and an interesting test of skill, as it challenges players to use lots of different types of weapons. Unfortunately it's also not always available to play - developer Sledgehammer adds it to the game every now and then (to the consternation of its fans).