Personally... no, I don't really care for Half-Life 2. I didn't get all that far in the game (the only aliens I recall killing were the ceiling barnicles), but the game just never clicked with me.
On the same token, however, the original Half-Life is one of my favorite games ever, and one of the few FPS games that I actually enjoy.
For a long time, I wasn't quite sure why I didn't like Half-Life 2, but now I think I understand why. It's the tone. Half-Life was a very lonely game. After some brief conversations with scientists at the very beginning of the game, you were basically alone for the entire thing. I really liked that.
But in Half-Life 2 (at least as far as I got), you never REALLY felt that alone. People were everywhere, everything took place outdoors, all the loneliness and claustrophobia was gone.
I guess I just found the second one lacking the atmosphere that enchanted me so much in the first.