Some early impressions:
This game actually isn't an immersive sim, but more like Outer Wilds + Hitman WoA trilogy if I'm trying to reach here. There are 4 areas with different locations where you can find various clues both related and non-related to the main 8 targets. Day-night cycle plays a huge part here, some targets will only appear in a specific location at noon, another might work at a facility in the morning, and two targets might meet somewhere at night. Enemy placement also differs at night, much more roaming guards and turrets, which makes sense because... the Visionaries party at night. It's more handholdy than Outer Wilds at this investigation aspect as everything you learn is neatly put into the journal but it's really needed, trust me you won't be able to keep track of them all just by memory.
One thing the game is really good at is giving direction to players and this is where I'd recommend turning off objective marker for a few reasons. First, there's these typographies that appear in the environment that looks like Colt's inner monologue, they can often tell you which one is the wrong way and hint at what you're looking for once you approach a location. Second, the objectives themselves give clues to where you need to be, for example, an early encounter with Juliana had her tell me that my flat is on the second floor next to the cliffside. Some locations that you aren't familiar with gonna take a while to find out, like a boatsman building at the far end of the island. Each time you enter and exit a location, time passes, but you can choose to advance to noon or night at the preparation menu.
There are of course sidetracks that you can stumble upon organically. I walked into this underground tunnel and found a strange dude behind a glass panel, ended up with me turning the wrong valve and I died from poisoning. That's where the loop comes in.
Weapons come in color-coded tiers but they have distinct modifiers, not different stats. So a hand cannon can shoot poison or deal more damage against marked enemies. Trinkets are like Dishonored's charms but for guns. Quite early in the game you can do a mission for the ability to infuse - keep your gear the next time you die. I haven't died yet so I don't know if you get to keep ALL the gears you infused in the last run, but considering the game allows you to infuse lots of stuffs, I'm pretty sure that's the case. To infuse you need a resource called residuum collected from items with anomaly effects or killing Visionaries. Residuum resets once you start a new run.
There's this mechanic whose name keeps escaping my head. When you're fatally killed, the game teleports you back to a location that you've already been through and continue doing business. There are two charges of this. The first time I died from falling into cold water, the game really teleported me to a moment where I was mid-air jumping between ice blocks and I felt again. Ironic for a guy named Colt.
Slabs are Dishonored-like powers, mana always regen to maximum so feel free to go wild, keep in mind there's no mana vial for instant fill, but you can equip a trinket (I think?) that can trade health when your mana runs out. Slabs also reset each run like normal gears and you can only get them from Visionaries. Killing Juliana in PvP always net you the Slab that the other player had equipped and shit tons of residuum.
Juliana has a separate progression system where you level up Hunter ranks to unlock new gears and slabs. She starts with Billie Lurk's Semblance that allows you to take the appearance of an Eternalist you choose. There's a list of challenges you can do to level up Hunter rank quicker. PvP in general is pretty fun, I had one trying to chase me through the first location just to fall off the cliff. The lag is unbearable though, two players slicing each with melee and the game might have a hard time deciding which one hit first.
About the most noticeably bad part, yeah the AI is expectedly pretty stupid, you can execute one enemy and the one right next to them wouldn't hear a thing. Going loud might be a bit more challenging since guns do hit hard, but again, the enemies are pretty easy to cheese. Keep in mind this is early game so dynamic difficulty hasn't kicked in yet.
Voice acting and dialogue are really good and hilarious at times. Colt's actor plays a confused cartoonish murder machine really well.