I can’t speak to all systems or configurations, but my desktop is Arch-based with the Nvidia 535 driver (a few versions old, I’m still waiting for the explicit sync driver support), I run the game through Xwayland (no gamescope), and I’ve been using protonge 9-2 as the compat tool. The game runs really smooth in my experience, and on protonge 9-2 I don’t have issues switching windows/workspaces.
I do run the game in exclusive fullscreen— I recall the window having a single white pixel border in borderless fullscreen.
You get medals and requisition points from playing that you can use to unlock new stratagems, which includes everything from weapons to orbital bombardment. Medals get you new weapons, cosmetics, etc. You also find samples you can collect on missions, and these unlock permanent upgrades for stratagems. There are player levels, but these just unlock new titles once you get past the basics.
The battle pass equivalent is Warbonds, which include new weapons, armor, cosmetics, etc. Unlike most games, warbonds don't expire and you can find enough premium currency while playing to get them without too much trouble.
On the whole, new warbond weapons tend to be different rather than obvious upgrades. The default assault rifle you get stays perfectly viable throughout the game.
Hope you have fun with the game! The only thing that's "weird" that you should know is that the battle pass mechanic in the game is not like most games. There is no time pressure, so you can always access any pass at any time. You can earn plenty of currency in game, and there's no "must have" item in any pass, so I wouldn't recommend spending any real money to buy the passes.
If you're a collector and into that sort of thing, then go right ahead. I just wouldn't feel obligated.
Even then, all unlocking the warbonds do is let you buy the items in it with the currency you can only get by playing
Honestly, by the time you've gotten what you want from page 3 of a warbond, you'll probably have already collected most of the super credits needed to unlock the next anyway
I remember playing splitgate (halo with a portal gun) had a battle pass and while the game was fun that BP and fomo was really stressful sometimes so that’s good to hear!
The difference here is splitgate stuff was (afaik, only played a tiny bit) all cosmetic. The helldivers passes actually do have different weapons and armor so it does change how you play, but most weapons are viable, especially at lower difficulties so try out everything and see what you like. But again, absolutely no time limit on anything in the game except the super credit store (which is just extra armor and it rotates through a normal cycle) and the missions themselves.
Just some very general tips so you aren't too lost. Enemies can call for help. Bugs rear up and bard orange pheromones into the air. Bots shoot a flare. You can kill them before they finish calling for help. Some enemies have armor. If your shots bounce off, try hitting a different spot or use a gun with armor penetration. 380 barrage is useful for big enemy bases, but tell your teammates. It hits a BIG area. Difficulty only changes what enemies spawn and how many. No changes to health or damage.
Also even the earliest unlocks are usable at the highest levels, so don't worry about using "noob" stuff.
It’s fun and has interesting mechanics. I found it to be a good game if you’ve got a group of friends to play it with. I got about 30 hours in until it got repetitive.