Well I just got round to playing HL2 alpha (if your gabe newell and reading then no I didn't play it or download it) and also Doom 3 beta 2 (better working alpha, if your John Carmack then same as with Gabe)...
Well anyways after playing both I have to say there is a clear winner in atmosphere, graphics and effects... Doom 3 kicks HL2's butt! HL2 is dissapointing, the videos look good but when you play you realise that its just HL1 with a higher poly count which they use up on larger maps, and some cool ragdoll physics. Doom 3 however... the lighting is amazing, the atmosphere scares me (especially with zombies getting back up and stuff) and its quite interactive.
Now you'll probably say Doom 3 runs like a man with no legs, but on my PC it runs pretty fine, only goes slow when I meet several enemies and have my torch on (real time lighting chews up your resources). HL2 runs perfectly smooth apart from at really complex areas (which I have to say arn't frequent).
All in all my vote goes to Doom 3 being better for Single Player, but for Multiplayer I think HL2 will be better purely on the ease to edit HL2.
Anyone here played Doom 3 Beta 2 and HL2 Alpha?
[addsig]

. Hl2 alpha is great, I had the 1000 uncompiled maps for awhile, but now my Alpha and such are all uninstalled. You can also play online with good `ol /connect 
