Hopped on last night and did my first runs on the Bunker map. This is all indoors, low-light, corridors, corner clearing, gunfire reverberating through the halls. Each map is rated for difficulty, and this one is four skulls, the hardest of the three current maps. But I think its probably the easiest, because if you play smart it is hard to get flanked or surrounded, which can happen more easily on the open maps. And the loot on the map is better. Better weapons carried by the enemies, more resources (concrete, food, oil, metal for safehouse upgrades) and a lot of the health injectors, which are scarce on the other maps. So don't be like me and put off the Bunker map. Hit it early and often. Raids are faster here too as you fill your loot bag faster, so more can be done.
One thing I really like about this game (and it's the same in most extraction shooters) is how firearms are implemented. The customization is really high, all the attachments. Of course you run the risk of losing that weapon, which is great when you think about it. This adds tension, and changes your mindset as there are no mulligans. Take a round through your noggin and all that gear, time and effort to trick out your weapon is gone. So you'll be more cautious, more alert, and each decision is final. And the weapon roster is already quite extensive and is growing all the time. If you like firearms, this a is a good game to get. Rails, flashlights, lasers, suppressors, all manner of optics and iron sights, thermals and NVGs, alternative mags and more. Some attachments require other attachments.
It's a job to find, buy and acquire all this kit, and to take it in the field with it all at risk is a nice hook.
I've been using a number of weapons, but I've taken to the Sig Sauer MPX, a 9x19 SMG that's as much carbine/assault rifle as SMG. IRR has an extensive roster of real-world weapons with real-world names.