The best action games like Left 4 Dead 2 are Back 4 Blood, Killing Floor 3 and Deep Rock Galactic. Below are 9, each with the reason it is here — and, at the end, what filtering to action costs you.
Filtering to action means you want the fighting to carry the game rather than the story or the map. It is the right filter when what you actually miss is how something felt in your hands.
What you get: Combat you get better at. Action games put their design budget into the moment-to-moment, so the thing you are doing in minute two is the thing you are still doing in hour twenty, only better.
What made Left 4 Dead 2 worth playing in the first place is covered on the full list. This page is the action part of that answer, and only the action part.
By the original Left 4 Dead team, with a card system layered on.
Wave-based co-op survival with the same close-quarters panic.
Four-player co-op with a director that escalates, and the best community in the genre.
Co-op against overwhelming numbers, and friendly fire keeps you close.
The closest direct copy of the four-player campaign structure.
Left 4 Dead with melee and rats, and it is excellent.
The current version of that formula, with better shooting.
If you want the tension turned all the way up and stealth to matter.
Four-player co-op where the plan falling apart is the fun.
Pacing and world. Action games rarely have the quiet stretches or the writing that the adventure and RPG picks bring, and a few of them are shorter than they look.
The full list is on games like Left 4 Dead 2 — 9 picks, no genre filter.
Back 4 Blood. By the original Left 4 Dead team, with a card system layered on.
No. Left 4 Dead 2 released on the Xbox 360, but a recommendation is only useful if you can play it, so the picks above span platforms and eras. What they share is the genre and the reason.
A small set of verbs and a game that keeps finding new questions to ask of them. The weak ones add buttons instead; the strong ones make you better at the ones you already have.
No, and difficulty is a poor proxy for depth. Some of the hardest action games have very few decisions in them, and some of the deepest have a difficulty setting that lets you meet them halfway.
By hand. Each pick was written for the full Left 4 Dead 2 list first, on what the game actually does, and this page is the part of that list that is action — never a genre tag lookup, which is how "best racing games like Super Mario 64" used to be a page on this site.
Or read the action guide for where to start in the genre generally.