TLDR Version:

Skill trees have been simplified in order to make it easier to read and understand for both old and new players.
New chase system – Cops will now chase you with their vehicles. New and old quests will also have enemies pursuing you. Aggroing enemies in the open-world can result in chases.
Vehicle combat is great – You can now aim and shoot out of vehicles. You can also use quick hacks that’ll cause other vehicles to steer in different direction, come to a stop, and even self-destruct.
New weapon mounted vehicles are available, some equiped with machine guns, other rockets, and sometimes both. We’re sure modders are going to have fun making Twisted Metal inspired vehicles.
2.0 Police System lives up to expectations.
There are five wanted levels, instead of four.
Police no longer spawn out of thin air, but instead will now drive out to your location with radio chatter playing of them coming to you.
Each wanted level offer different tier levels of police. You’ll see normal police, armored ones, elite, robots, and of course the Psycho Squad.
Different tiers of vehicles also start appearing, those being your standard squad cars and motorcycles, to armored trucks and weapon equiped ones.
Maxtac (Psycho Squad) have a unique spawn animation – They are now flown in via airship, and drop down from it.
The police have access to hacks, can pinpoint your location and even disable your vehicle.
On foot cops will chuck grenades at you to try and stop you.
They will barricade roads ahead of you if they’re in pursuit.
If they have you pinned on a street, they will start to surround you and block exits with their vehicles. They’ll do this, even if it means ramming into one another. They’ll also use the vehicles as cover.
City turrets appear to be gone, though I could be wrong.
All these additions make the cops feel like a true threat to the players, unlike before where they sort of just existed.

We think there's more traffic on the roads of Night City, which could have something to do with the implementation of car combat and NPC AI improvements
Some important character models have been improved with better facial details, Johnny Silverhand in particular
Key boss fights have been adjusted to make them more unique (and potentially challenging)
We found a few new weapons scattered about in main missions, and stumbled across a couple of iconic weapons we hadn't seen before
A large number of persistent bugs appear to have been fixed, including clipping and animation issues with some characters during story scenes
Your equipped healing item is now infinite, but operates on a cooldown (and can be upgraded)
Grenades are also infinite, but have a cooldown
We noticed a lot of new clothing items, in many more colours than before
There's a lot of new cyberware which better represents the type of character build you're going for
MaxTac have been given a visual overhaul

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