if you want to go in totally blind please don't read. (I won't spoil any story stuff though)
I've played about 3 hours. 2 of those 3 hours was what you could call a "tutorial" where the game mechanics are explained simultaneously with Lincoln's backstory. It's done really masterfully imo and has you jumping around time while having bits and pieces foreshadowed that you then play through. I have spent very little time with the actual open world (the first 2 hours you are guided through the missions with little to do if you stray from them).
Things I Really Like:
the weight of weapon impact - shooting people feels really nice, they react when you blast them in the face with a shotgun in a satisfying way, and the knife kills are also quite satisfying. There is a real sense of presence when fighting enemies.
for those who played Uncharted 4, conversation resumes organically after getting back into a car - just a little thing that speaks to the quality of the game
the story/voice acting/writing - I'm no expert in this stuff but I play a fair amount of games and this all seems very well done. I'm more invested in Lincoln's story after a few hours than I have ever been invested in the entirety of other open world games like Mad Max or Far Cry for example.
there are a lot of really cool collectibles - I'm not going to say anything about these but they're much better than your standard bs "random item that is important" or "random stock artifact". They matter to the time period and show the dedication of Hangar 13 again.
the music - AMAZING TRACKS. I'm 20 and love love love the music. For the older folk out there I'm sure you'll love it even more than I did.
What Wasn't Too Great:
lots of pop-in - specifically when driving, cars would pop in on the road ahead of me. It was never bad enough to the point of me crashing into them, but it's noticeable. In no way does it detract from the experience though.
From what I've seen so far there don't seem to be many upgrades to Lincoln other than generic "improved health" and "carry more ammo" and that disappoints me cause I love RPG elements in games.
frame rate was pretty unstable for the first 30-40 minutes of play time. It dipped quite often but since finishing the very early "intro" "tutorial" whatever you want to call it, it has been steady.
stealth - enemies don't notice you when they can clearly see you. It's pretty immersion-breaking to bolt out of cover to another cover point and an enemy is looking your direction but that stupid "enemy is seeing you" bar is just slowly rising and then you tuck behind cover again and the bar goes away. Good thing shooting people in the face is nice
I have only just scratched the surface of the game and am just entering the real open world parts of it. I love how the story is being told so far and the characters are really great. Gameplay seems to be standard fare so far but the time period, atmosphere, music, and authenticity of the world are really really awesome.
Ya'll can ask whatever questions you want in the comments and I'll do my best to answer them. I'm going to play for a few more hours later tonight so I'll have a much better idea of what the game is really about then.
EDIT: 6 hour update
mission structure is insanely repetitive.
weapons are not very varied.
melee kill animations (while satisfying) are not varied enough to keep the satisfaction rolling.
story and writing continues to impress.
not much to explore in the city, basically driving from this "kill everyone" mission to another "kill everyone" mission.
I initially loved the collectibles, but now I'm realizing the only incentive for me to explore the boring buildings of the city is to see naked girls in the playboy magazines
3 hours = 'holy shit this is amazing', 6 hours = 'I wish there wasn't so much gameplay in between story beats'