The installation process probably takes about 20 minutes. The DVD unloaded it's contents on to my machine, which took a while. Then I had to set up a Steam account and let it verify my installation, which took a while too. Eventually, it was complete and running.
First, the software isn't buggy any more. With Half Life, whenever I drop back to the desktop, everything is smushed together, and sometimes windows won't want to be selected, or web links fail to work. Screwy? Yes. But then, I'm using a relatively unpatched version of the game. With Half Life 2, it transitions between the desktop and the game without glitches. I accidentally hit the Windows key a couple times at first, and I was able to go back to the game right where I had left off. In Half Life, that would have been pretty much a guaranteed reboot.
With that out of the way, I can say that Half Life 2 is the best looking game I've ever played. While the graphics of Myst are probably somewhat out of date these days, my description would be something along the lines of walking through a Myst-type world in a FPS style. The gameplay is also quite good. The sound effects are good, the BGM is generally non-existant, but the world has it's own living sounds to fill in the void.
The one dissapointing thing is the lack of multi-player. Playing the single player scenario is quite good, but I want to be able to use these weapons and the new physics engine and kick people's ass in it. On the other hand, I'm confident that multi-player mods will be released within a fairly reasonable amount of time, so I don't feel too bad about the lack, since it's going to be mitigated soon (I hope!).
I haven't completed the game, but from what I've played so far, this is definitely an A+ level game.