It's my favorite game also. Hl2 depicted an enormous dystopian future. Sterile humans and depleted oceans only scratch the surface. The gameplay is classical but very engaging. As Torjan211 mentioned, Alyx was not a big boobed eye candy support character. She had depth and realism. The game was not trying to sell sex…

It was a misstep, surely. They saw a successful game and pounced on the developer, seemingly having no idea if they'd ever strike gold again.

I would say Half Life 1 wrote the book on seamless story/gameplay. The other reasons are good reasons. I love the Gravity Gun. While other games have telekinesis and stuff, it never feels the same.

*insert obligatory "shut-up and take my money" quote.*