There is not one mechanic that was changed in this game that I like. The regenerating health sucks. In the first game getting hit by a stray bullet was noticable, here it's NOT getting hit that's noticable, because if one or two bullets from an entire magazine do not hit you, you can just run-and-gun into the enemy with no repercussions. Submachine guns feel better here, but the rifles suffer a good bit. Maybe I could enjoy this change if they didn't remove the quicksave feature. I'd be more than happy to charge in if it didn't mean going back several minutes every time. No idea why the sprint from the expansion pack was removed (especially since your allies can sprint but you cannot) making the checkpoint system even worse as you have to slowly get to the point you already were in, but due to the incosistent enemy behavior you sometimes will die retreading these steps. The levels are also much smaller and shorter, you can see this especially during the defensive ones. The Soviet campaign ends with something akin to Pavlov's House from the original, but instead of the building you defend being several stories tall, here you have two rooms one each floor, two floors total, and a staircase next to each room. There's just not enough space to maneuver. Also, one of the biggest selling points of Call of Duty was moving together with your squad, I think, but here your squad is trash and cannot shoot enemies standing right in front of them and nobody is checking their behinds, meaning you will occasionally get killed by a random enemy who spawned behind you or didn't peek their head before. And possibly the worst thing is the grenades spam. Some chokepoints are just annoying in the worst sense of the word, super unsatisfying, and on harder difficulties alternating between running away from grenades and running into cover after getting shot once means you can spend way too much time on one checkpoint.
Also, why in the world does a sidearm take up an entire weapon slot now? You move much faster with it so it could totally fix the sprint issue, but it takes up as much space as an anti-tank weapon apparently?

As for additions, I like the multiple objectives in theory, but these missions tend to get more frustrating than anything due to the endlessly respawning enemies. There's apparently thousands of enemies just behind each objective that disappear when you walk next to the building's window. Also, nobody secures the objectives you already captured, meaning that the AI who runs there will still run there and you will, again, get shot in the back. Smoke grenades are my favorite addition, they allow for cheeky plays like running through the smoke to catch enemies unaware provided you know their positions, because they do not move.

Game could still be fun if it had larger levels, there's still that great sound design and those good feeling guns. Some okay bits but largely I was just reminiscing of the better missions from the original. Big ups for being able to throw potatos at NPCs in the tutorial, best part of the whole experience tbh.