What are the best multiplayer games to try if me and my friends are looking for a similar experience to a Bungie Halo campaign marathon on Heroic+ difficulty?

Gears of War comes to mind, not much physics but a lot of emphasis on movement but in a different way from Halo, still stupid fun to play the campaign Co-op!

The borderlands series. Start from the first and work your way through the franchise. I'm not a huge fan of the latest games but 1 and 2 have at least 60-80h of gameplay I'd say.

The Half-Life franchise, maybe. Half-Life 2 and up has a lot of physics stuff including the Gravity Gun, but considering HL1 is free to play via Sven Co-op it wouldn't hurt to start there. You'll need something like Synergy or Obsidian Conflict to play HL2 cooperatively.

If you're looking for a shooter, co-op campaigns for those things dried up a while back, so you're mostly looking at older games. My friends and I are playing Quake and Quake II to scratch that itch, but those old shooters are also very maze-like. If you're open to suggestions beyond shooters, I'd recommend a couple of roguelikes, namely Streets of Rogue and Vagante. Both are very chaotic, sandbox-y, challenging, and scale really well for co-op.

I would recommend something just outside your area but with a lot of fun movement mechanics.

Warframe It's an online/instanced 3rd person shoot em up but the movement is the best out there. PvE focused but there are PvP elements too. Very good and long progression but it is grindy.

Titanfall 2 The campaign is single player but one of the best told stories. The movement is just behind Warframe. The online multiplayer is absolutely epic as you get to take out Titans and also call down your own. However, there is quite a lot of cheaters unfortunately which may spoil your experience.

Closer to your request.

Orcs Must Die Fun tower defence with traps and 3rd person action.

Deep Rock Galactic Mining space dwarfs and beer. That is all you need to know.

Gunfire Reborn Roguelike FPS with lota of characters and abilities. The aim is to kill the final boss and then try to do it faster and faster.

Got more if you want to know more, but that will be a very good start.

Reading your post and then reading the replies made my chest hurt lol.

Bungies halo campaigns were just something special. I don't know when we'll see a co-op fps at that level of quality again. Those titles have lived rent free in my brain for the past decade

One thing you could do, depending on how much you and your friends enjoy a challenge. Is to do the halo 3/ODST Vidmaster challenge. My friends and I did it together twice when it was first released and those are some of my fondest gaming memories

The Division 2. Also has raids. Just prepare for some bullet sponge.

The obvious suggestion is Destiny 2, it's a coop Bungie shooter with emphasis on movement. The expansion campaigns are fun and challanging on Legendary difficulty. Only thing it's missing is the physics sandbox.

Epic is currently giving away the the Legacy collection for free which has three of the four current expansions. Absolutely worth grabbing and giving a go as I'd recommend to anyone starting the game to just focusing on going through the campaign as you'll probably have a good, if confusing, time. The big downside is the fact you get thrown in half way through the second game in the serise so if you want to understand the story you will need to look things up.

Deep rock Galactic is my vote. It doesn't have a narrative, but it does have a very thin campaign. It's mostly a few voice overs and random missions. However, the difficulty is scalable, if you're looking for a challenge. The game is incredibly movement focused. Each class has a movement power that's unique. Gunners get zip lines that are slow but go up and anyone can use them. Scout has a grappling hook that's fast and unlimited but only they can use it. Engineer makes platforms that anyone can scale. Driller can tunnel thru the rock any direction. The terrain is deformable.