People don't ever seem to clue in that (and I know this will sound cocky of me) when a company produces a design document for a game it usually means that they'll stick to it until the game is finished.
Half-Life 2 has been in development since the day that it's predecessor hit the shelves and after seeing the movies I can tell that I'll be happy to play it. Don't think I'm playing up HL2 as the Doom killer (though it probably is), what I'm saying is that DX2, Thief3, and HL2 have all been following a set script for the past years. Just because it's set for next year does not mean that id Software has re-thought their approach (they could have gone back to the designing board, but I doubt this). I most certainly do not believe that id Software is re-conditioning their game as a Half-Life killer. The folks at id Software will make sure that they create a quality product based on their own intentions and Activision (for once) does not have the power to rush them. Thus they're taking their time thorugh the design that they've already created.
Now that that's all said, I'm looking forward to HL2, DX2, Thief3, and Prince of Persia. To me, these look like the instant classics of the next generation.
Oh and one more thing, folks, keep in mind that Valve plans to re-release every popular mod currently using the Half-Life engine and will see that modders have a full toolkit for converting their mods from HL to HL2.
Let's see id Software bring out those kinds of guns.