It does make sense. And the physics is downgraded to non-existent than in HL2. The Physics calculation is done server side so they can't be as advanced as a single player game which is done on your machine. The server has to do AI, physics, audio, scripting and a whole host of other things. Server renting is expensive and making the server requirements to high would make the make it too expensive for people to run public servers. You also have the lactancy issue. More physics equal more lag, but lets look at the plus side. Left4Dead introduced physics-based animation which realistically portrays hair and clothing, and improves physics interaction with enemies when shot or shoved in different body parts. This new Physics animation allows characters to lean realistically when moving in curved paths something Half-Life 2 doesn't And the water is also worse than in HL2. I disagree, but one thing Valve have said is that water is very expensive resource wise. For example the elevator battle in Episode 1 was meant to be in water, but the water was removed for more zombies. And the weapon animations and motion is worse than in HL2. I again don't find it worse. The animations may be quicker but that's because Left4Dead is a arcade type shooter unlike Half-Life2. And there is clipping all the time, you can see zombie hands and heads through doors and walls. Half-Life 2 suffers from this as do most other games. It's takes to many resources to prevent it happening which could be used on other things. And often you see zombies levitate. Can't say that i've ever seen that happening. And there is no story or narration devices. And so on, and so on... In typical Valve style the story is not fed to you as in other games. The story is there you just have to keep playing it and put it together. If you are to lazy to do so then that's your problem.