In the first game we had nice creatures and it evolved around a different reality. There were cool labs and military places with intelligent cool soldiers.
In HL2 we have ugly stupid boring humanoids, a few nice creatures and really boring environments. All the time I was waiting for the fun places to come, but it never did. Few and really boring weapons. In HL1 and it's expansions we had nice energy and alien weapons. The gravity thing is just some boring toy. I don't see why people see it as a special and funny thing. It's something you would have to use for some puzzle and then leave it. It's not something important. Even worse was in the end when you only had the damn thing with a little bit modification.
Sure shooting saw blades at zombies is fun for a few minutes but it gets boring because you can only split them on one specific part of the body. If you can remove body parts at all in a game then it should not be limited like that. The model should be able to split on many places depending on where the player aims. It doesn't need to be Solider of Fortune but at least 3 splitting areas. And btw the fact that bodies doesn't blow to pieces from explosive is unforgivable, like in so many other games since physic engines and bump maps. I don't lust for blood very much if you think that but weapons should still have enough realistic effects. I don't remember but maybe bullets didn't create blood decals on the bodies either which is annoying as well.
The only really good thing in HL2 was the different types of head crabs.