>>545987771
Yeah, it's Steam Workshop compatible too. You just pick a mod, press the subscribe button, and it downloads and installs automatically. Every game in Masterchief Collection (1-4, ODST, and Reach) is moddable. And there's official mod tools for them.

There's a ton of stuff. A bunch of canceled/cut content from the games was also released as a mod pack, and you can go through and try out all the weapons/vehicles and stuff, even from the original Macworld version of Halo before it came to Xbox. The Halo 2 E3 demo also got released as an official mod.