The problem is that all of these games serve different purposes using their engines so it's like comparing bananas to kiwis (just to be different

). FC is out now, uses DX9 fairly extensively, and is set mostly in the out of doors with large amounts of foliage and scenery. Stalker looks to be set outdoors as well, but is not out yet, could change dramatically before release, etc., and it's more of a dark and dreary setting (which is just about equally exciting to FC in most cases

). Doom 3 is amazing in its own right because of what it's able to accomplish with DX7 level effects using OpenGL, but again it's different from the other games so it's hard to compare because it's mostly set indoors and
very dark, with lots of spooky futuristic settings with a different kind of enemy than the others (can't wait to see the cyber-demons stomping around and the pinkies followed around by those goddamn cacodemons). Finally HL2 seems to be a mix of both indoor and outdoor more than the others (of course the rest do have indoor settings granted) and uses DX9, perhaps more extensively than any game but I haven't looked deeply into the shader usage of these games as I don't have the attention span for it

They all accomplish their intended values very well, but we will have to be able to play them to truly compare. From what I've seen, HL2 seems the most impressive, but it very well could be vaporware. Graphics abilities aside, they all appear to be fantastic games at a deeper level than aesthetics.