Nuclear Winter is pretty fun. It's a bottle game, so you don't lose anything on your character if you die. It has its own perk/leveling system and loot system. Pretty fun thus far. You do need to play with a mic, though, to get the most of it. I didn't have one hooked up, so I couldn't tell the guy who looted a nuclear briefcase that I had the nuke codes to use it. Apparently when you get both, you can nuke part of the map, so it's good to try to save it for the final circles if possible.
Basically everyone starts in the vault. You can change perk card loadouts/etc (it starts you with basic shit tailored for the game, but I guess you earn more as you go). Once the vault fills, there is a countdown and everyone chooses where to spawn. It isn't the whole FO76 map, just a segment of it. I am guessing in full release, they'll use different parts of the map to keep things interesting.
Bobbleheads/magazines give you immediate buffs, so they are worth picking up. All loot is inside containers and crates, except the magazines/bobbleheads. There are 3 special lootcrates. The big orange ones have the good shit in them, like heavy guns or instant-camps or nuke shit, and they emit a 'beep' sound if they have nuke codes inside. You can find power armor out in the world and they all have fully charged fusion cores. Stims/etc are there. AI Enemies are randomly around the map. Only thing VATS works on (VATS is disabled vs. players). They're worth killing because they can have loot/supplies. There aren't many circles, but the game lets you know when it's about to move and it moves fairly fast. Reviving downed players doesn't take a stimpack, but they only come back with like half health.
Once you die, you can spectate or see how much XP you got. Leveling up/getting XP unlocks new skins and new vault quests.
Game runs fairly well even with lots of players, probably because of various tweaks they made to loot (there's no junk/etc). I didn't really notice issue with hit reg. There isn't any bullet drop and the gunplay mechanics are still Fallout, so mostly hitscan. Sound could use some work, though. Both times I died, it was due to enemy teams rolling in on us and I didn't hear them (then again, clanging around in PA doesn't help since that probably makes it harder to hear enemies). When enemy players shoot you, they do get red triangles above their head (which helps, because it is REALLY easy to blend into your surroundings). I didn't see if they went away with time. There's no disease or food requirements, but radiation is still a concern.