I have to confess that I haven’t played H4lo, but generally speaking, John Chief is fighting an “ancient evil” on a “mysterious world”. Aside from the campaign, there are 25 multiplayer maps, plenty of armour options, and Spartan Ops, which is an episodic co-op campaign that carries on from the singleplayer story.
Beyond that, there’s now input-based matchmaking and crossplay for every game in the collection, meaning you can choose what device your multiplayer opponents have so you don’t bring a pad to a keyboard and mouse fight when console and PC players play together. Halo 2 and Halo: Reach also have specific updates that make running at 60fps (and higher) a whole lot easier. And though there are no more Halos to be added to the collection, development will continue. There are more features, such as file and map sharing, to come. It’s been quite a year for Halo, really. 343 Industries and Microsoft managed to release six games in less than a year. That should see everyone through until the release of Halo Infinite, which was delayed recently until sometime in 2021. it’s out now on Windows Store, Steam, and is included in the Xbox Game Pass.