Gravity gun opening up possibilities? I have to disagree slightly. IIRC the secondary fire was enabled nightvision firing. And the interactive environments add a new aspect of gameplay. But HL2's environmental diversity is one of the things that keeps me going back for more. I got pretty bored in Doom 3 because everywhere looked the same. I also prefer HL2's graphical style to Doom 3's. I can run HL2 on the highest detail settings with no slow down at all, while Doom 3 slows down a lot at some points. Technically it's a simpler game than Doom 3. Granted the pixel detail on a fair number of the textures is a little low, especially by today's standards, but Doom 3 also has the same problem, it's just it's often hidden by Doom 3's lighting and bump maps.

The still screens do not do the game justice. I'm much more impressed with HL2 than I was with Doom 3. But really, graphics isn't about what's happening on every pixel - it's about the bigger picture. Not once did I see anything in Doom 3 that had the same visual impact on me as the alien Citadel in City 17.

Gauss gun half life