grandstand pong? i suppose, as it's purpose was to play pong, it's a games console...
in my opinion there aren't any fps games with a better storylines (granted, i haven't played through the storylines in a while, and i probably won't until the day before halo 3 is released, but that's because i've been through them so many times). the multiplayer is good, as long as you're with a group of friends in a custom match. unfortunately there's so many modders playing halo 2 matchmaking it makes the experience highly degraded...
in the end it all comes down to personal preference. so what if i love it? that's my opinion and won't (or at least shouldn't) affect the opinion of anyone else. so what if someone hates it? that's thier choice and preference.
IMO, if you can get good FPS on Halo on your old PC then it can run any game on the market though not necessarily well.
(EDIT: i forgot how to quote...

)
my pc runs halo pc great, but i can't even get to the title screen for f.e.a.r... stupid nVidia MX420...

about halo 2 vista... it's just the same as having a sequel released on a better platform (like the final fantasy games from snes to psx). yes, there's some pressure to buy the new o/s or console, but there's always more than 1 reason for something like that... for example the final fantasy games went to psx instead of n64 because it was cheaper to produce the games on a cd then spend money on carts.
i don't deny that it sucks that i won't be able to play it on XP though.