Half-Life was being considered one of the best FPS of all time long before Counterstrike or even Team Fortress Classic.
I remember PC Gamer said it was the easiest Game of the Year selection they had ever done, since the entire staff felt it was (whereas usually it is hours of arguing and debating which game was game of the year). And it wasn't because of lack of quality games coming out either.
Half-Life 2 has not been described as more of the same. The game is supposed to feature some of the most intuitive AI, and promises a more dynamic gaming experience than Half-Life with less scripted sequences. It also sports an intensive physics engine, and the ability to generate real time accurate lip synching. Reading as many Half-Life 2 previews from magazines and websites, not once have I seen Half-Life 2 being more of the same.
Doom 3, while also having an impressive graphics engine, has not been hyped up for its "normal mapping." It has hype because it is supposed to be a story-driven (something new for Doom) game that tries to scare the **** out of you whenever it can.
I do not know much about Halo 2 since I do not own an X-Box. I remember adamantly following the development of Halo, from the Macworld demonstration that just blew me away. However I feel it lost a lot of its thunder because it got delayed too long. By the time I finally played it on the PC, it certainly was not the uber-cool experience I had hoped for for so long. The game is still fun, but its monotonous level design and mediocre multiplay left me wanting more. If Halo 2 comes to the PC then I'll look into it a bit more, but right now I don't follow it too closely.
However, time is starting to run short on HL2 and Doom 3. They at one time had people ooing and ahing over their graphics, but Farcry was able to beat them out with that.
On a side note, a lot of people this year list Splinter Cell 3 as Game of the Show over both Halo 2 and Half-Life 2.