I never saw that half-life 2 had so much more to add to game play compared to half-life 1, the only thing i remember was that you had car\boat you could drive around and a weapon that lets you pick up things to throw, like saw blades at zombies
Really there wasnt much it did do revolutionary in game play when it came out, alot of different more games were released at that time that did have more game play mechanics that half-life 2
CS:GO dosnt have all the new things, heck it is a very basic game compared to even TF, so new things are neat, but we can see that new things are not all that is needed to have a good game
I could go to say that maybe valve has a writers block for the story or the developers like mojang got tired that people(players) expected to have it all now now and as great it is in their(playes) mind that the developers got tired of it and said fuck it, I move on