Hit detection and lag compensation need major revisions. The game physics, in general, have gotten out of whack with recent updates.
- Bullets traveling through / around objects.
- Explosions killing you through walls / barriers / etc, even when you are standing multiple feet away.
- Hitting someone full speed, who isn't even looking in your direction, with a Ghost only to not kill them and instead have them hijack it.
- Duels where 6+ BR shots won't take down the laggy player who is jittering, but 2-3 of their BR shots will kill you.
- Shooting rockets, etc through players.
- Spartan charging through players without registering the hit.
- Melee weakly whiffing multiple times when you are literally touching the other player.
- Ghosts / Warthogs going on ridiculous wobble / tailspins due to invisible bumps.
- Spartans movement getting stuck on basic design elements, like slight inclines.
- Spartan charging someone standing still and not killing them, only to have them immediately Spartan charge you back and kill you as they are flying backward.
- Radar seeming to be the first thing to go out the window when the connection isn't perfect.
Also, there are certain power vehicles that seem to cause an overall frame rate drop on certain maps - like the Wraith on Viking in BTB, for example - which makes aiming and the controls go to crap. It doesn't happen every time, but it is fairly consistent, and seems to mainly impact the "power vehicles".
Lastly, in Warzone, how the server determines which team gets credit for an AI kill is a complete coin toss. I can't tell you how many times a game has been decided on the other team getting an AI kill credit when one guy fired a couple rounds at the very end while my team had a group of players/vehicles constantly firing on the AI. Those kills are too critical to team points to get wrong.
Adding one more that I experienced multiple times yesterday after creating this post - when players leave / join, I know it is normal for there to be a brief pause as the server recalibrates (for lack of a better word). What I've noticed lately, is it is not uncommon for gameplay / connection to degrade heavily after that activity. Ex: gameplay is okay, someone leaves, someone else joins, after one of those pauses everything feels laggy - like you are a half second behind everyone else - for the remainder of the game. I suppose lag compensation could be partially to blame if the player joining is on a poor connection, but it seems most likely there is something getting out of sync server-side as degradation seems to apply across the board.