How is Marathon, for someone who missed the Slam, and what is the progression and depth like?

I unfortunately didn't even hear about the game until now, and that was through a meme in the Arc Raiders sub saying you can like both games. I like extraction shooters, and was looking for a nice middle ground between arc and tarkov. The most embarrassing thing to admit, CoD DMZ was probably one of my favorites. So far, I've heard that Marathon has a high TTK and that's a plus for me. What I'm wondering is what is progression like, and the depth of systems in the game? While I like Arc I wish it had more in the way of progression and depth. Tarkov has a ton of this, which is my favorite thing about it, but it's plagued with so many other issues that I don't really find it as enjoyable anymore. So I'm wonder where Marathon fits in, in all of this, and if it would be something I would enjoy. I only really make enough to buy a game once in a very long time, so trying to get a feel for things before investing.