I voted A.I./Physics because I'm looking forward to using only the manipulator and grenades as much as I can to get cool stuff to happen... which will be made even sweeter by the A.I.'s reactions!
The new engine I'm also liking because:
1) It scales and is playable on average systems
2) The MODS man! (I even plan to do one!)
Uh... i dont know where you're getting that from, but Geomodding (used heavily in games like Red Faction) is using map displacement and someother technical crap so that...when you shoot a rocket at the wall, it'l leave a crater... in Red Faction Online, snipers often dig tunnels to higher spots and then have thier own sniping spot
i voted A.I / Physics because the AI are indeed very intelligent in terms of gameplay. Matches the nice interactive environment.
But i do say that HL2 doesent have that good of graphics, its mostly been impaired by the fact that (from the screenies) cylinders arent rendered properly, (they still look 12 sided unless its a thin pipe), and the interactive environment acctully causes lighting problems within the engine
What can I say? I loved the HL1 AI, and HL2's is way better even, plus the physics, those 2 factors really convinced me. Plus of course, it's sequel to HL1 which is already enough reason to buy it, plus it's HL universe, like Mr.Magnetichead mentioned.
I vote other.....its not each thing individualy that are cool becuase they have all pretty much been done in some form or another.....its bringing all of them together that is cool IMO.
This poll should have been called "What aspect of HL2 are you most looking forward to?"
Personally, I'm really looking forward to an immersive gaming experience, and getting drawn deeper into the plot. That's what I loved about HL, and I'm sure HL2 will deliver.