Ok, let me explain, HL2 has great puzzles and atmosphere and game play elements like the gravity gun and other quirky weapons, but none of these reasons are what makes me play a shooter. I love mass scale battles with 30-40 really though enemies at once, vehicles and a smart AI shooting at me from all fronts. In HL2 I never get this. All events are scripted and its always the same fight, soldiers always showing from the same angles and always playing the same. Also, the encounters are very small and it sometimes feels like they are just there to be filler between the puzzles or test out your overpowered weapons and bring them down like flies. This is why I do not like HL2 as a shooter. I do not like it as a game at all because it is strong in the aspects of the FPS genre I care the least, but is weak in the aspects that I care the most. I hope that explanation is satisfactory.
I realized that a couple weeks ago and since then my hype started dying. I wish somebody would make something like a Halo RPG. A game with amazing battles like Halo, but with RPG elements (navigation through a world, chatting with NPC's, sidequests that are not required, etc).