It is pretty literally Helldivers 1 in third person, which just makes it even more chaotic because now things can sneak up on you. If you found the first one too difficult this is just as hard, if not more so because of the camera change.
Had to check if this was a throwback to the 2006 game of the same name but it appears to be unrelated.
My understanding is that the first expansion fixed many of the launch issues; I played it a ton in between the second and third expansions, and while it wasn’t a AAA game, it was still a very enjoyable sandbox. Watching the IS map evolve over time was great, and eventually the whole thing turned into 'mech Pokemon, which I got sucked into but could be very dry. It was pretty far from MW3’s crafted campaign, but the first expansion did add a number of short and sometimes memorable mission chains all over the map you could run into, giving a bit of that campaign story experience. The second expansion added another campaign you could choose to pick up, but I never did so I can’t comment.
You’re dead on. Sadly the game never explains it but you’re really not meant to shoot everything on the map and that’s what every new player is doing right now. Navigating around patrols to reach your objectives and knowing when to disengage and circle back when you’re being overwhelmed are the real core of the game.