Big Metro fan here, so yeah, I get where you're coming from. It's been a few years since I played Misery, so sorry to say I can't answer your questions with err, clarity. There are a number of new weapons, of all classes They say 200+, but I think that includes all variations of the same weapon. There are many new items. 'Kit' has been completely overhauled. Finding items is a big deal. For example, there are aluminum frames you can acquire to insert in your bergen to increase the load capacity. Ammunition has to be husbanded. Misery gave me a different feeling. My base was aboard a ship, and before each sortie, I got the sense I was laying out my kit for the day. If there were a mirror I'd probably get my gear on, look in the mirror, deep exhale, lock and load and say out loud 'Let's do this'.
You can download a PDF here to see the weapons
http://www.moddb.com/mods/stalker-misery/downloads/weapon-appendixOverview of changes
http://themiserymod.com/index.php/introduction/When I played, I didn't really do much story stuff. I just played it like I was a STALKER, leaving the sanctuary and venturing out to see what I could find, with the goal of returning by nightfall. It was a lot of fun.
There are blowouts, you get a short warning of a few minutes, a siren I think. You must seek shelter or you die. More than once I died while opening the door, just needed a couple more seconds
Stuff is more deadly. Nights are dark. Sounds are creepy. You start in a random spot I think, with nothing but a rusty gun. I was in head-high reeds, and there were things moving around I couldn't see. It was scary. When I first saw the ship I was quite relieved.