There are two types of floors - the slimmer floors with crossbeams in them are shoot-through. The thicker floor types that are solid and you can’t show through them. Your aiming beam, if you have one, will show you if the beam is passing THROUGH the floor, you’re good. It works for both you and enemies the same way.
Can shoot through:
Cannot shoot through:
You can only ignore/shoot through obstacles you are adjacent to. Get right up next to a barrel and you can ignore it, which is how I like to take out enemies behind barrels.
A lot of launchers have the modifier “arcing shot” - stuff with arcing shots I found really hard to use, I started using launchers that didn’t have that to more reliably hit my target with those weapon types.
Look at the abilities of a character with (iirc) X and you can reiview their skills and weapon types. Everyone has two, like “handgun” and “something else”. I almost never use handguns - no scopes on them. My go to four-man team used an assault weapon type, heavy weapon type, sniper weapon type (sharpshooter with long range; cannot shoot if you move that turn), and sharpshooter pistol (works like a handgun, but with a long range scope).