I agree that Half LIfe revolutionied the FPS in a way. This was the first game that was seamless. Play right through, no levels to load, no breaks. You were in a world (or worlds) that had no 'end of level' areas or anything, you got done storming a complex you walked out and found your way to the next place. The graphics were top of the class for the time (remember we're talking about quite a few years now, and it still looks good) and the AI was phenomenal. Halo is a glorified half life and that's all it will ever be. Now don't get mad at me, I loved halo and it will remain a classic.
Like was said above, though, the original half life was designed to run on a Pentium I. Half life 2 will be designed to take full advantage of the absolute latest processing and graphics technology, while halo 2 is stuck on the same 733 MHZ celeron, 64MB RAM and Nvidia GF3 that Halo1 was written for. Yes a PC has overhead. But your standard PC has at least 4 times the ram and CPU as an xbox, and you can't upgrade an xbox (well you can get to 128MB RAM and a 1.4GHZ cele, but it's next to impossible for the average gamer, and even then the game is still written for the standard xbox, you can't increase the resolution so it's a waste of time). I got a 2.0GHZ P4 system with 512MB RAM and GeForce4 for $500 last summer. The same system can be had for less than $300 now (xbox price territory), and it will blow away any xbox, or any console.
I am really waiting to get a hold of Doom 3 and HL2. I will definitely also own Halo2, but it is the least anticipated of the three. The only thing I'm really looking forward to in Halo2 is the storyline, whereas I know HL2 and Doom3 will be visually and physically stunning.
I have been a PC gamer since a PC was a Commodore 64. I know my games. No offense, but most of the people on this forum are kids with xboxes. Not a bad thing, but they can't really appreciate how far we've come. I remember literally dreaming about playing a game that had graphics that were even recognizable, let alone life like, and now here we are. It seemed like an impossibility, yet it is as real as this post I am typing.
Well I'll get ready for the xbox fanboy flames, but all of you that are in it from the get go like I am know that the consoles will always be limited by their very nature, being non-upgradable and designed to meet a profitable price point. Halo 2 will be good but any reasonable person will see the disadvantages inherent to the xbox.