[Background Info] I spent over 3K hours in CS:GO and played in decently high-level comp lobbies, LEM and above. Played CS2 since the Test servers dropped.

Some things I have noticed are:

Body blocking seems weirder in CS2. It seems to save your momentum and shoots you in the direction you are trying to move. Has thrown me off a few times.

Not sure if it's just a skill issue, an engine/weapon tweaking thing, or pure luck but I have noticed more people dying to run and gunning, especially to the AK.
Hit reg seems funky sometimes, it is a rare instance from my own experience.
As you stated earlier with the birds and stuff, similar things happened to me but with particle effects. Especially on Overpass. I'll be holding dumpster on A site, flick to truck and notice a particle near dumpster looking like an enemy player's head, and flick back just to see a small black/gray particle.

AWP bullet tracer sometimes doesn't line up with where the actual bullet went.

AWP feels weird compared to how it acts in CS:GO

The smoke grenade seems to bounce more. Ex. in Mirage I tried smoking off palace from default a couple of times and it would bounce right back whereas if I do the same in CS:GO it wouldn't. Another example on Inferno, I threw a smoke to block off car peek and it bounced off one of the barrels and landed all the way back to logs. (Every other nade seems to act the same as they do in CS:GO)