You're comparing the wrong engines. The Unreal engine as it stands for Ut2k3 and u2 is not meant to compete with doom 3, it can't. It does look better in some ways (outdoors, etc) but the doom3 engine is far superior in capacity and effects.
What you want to be comparing is the doom 3 engine with the Unreal Warfare engine, which will definatly give Doom 3 a run for its money, seeing as the current engine does hold its own against doom 3.
Both Doom 3 and Unreal "warfare" will be out around the same time, which is mid-late 2003.
Comparing Current Unreal Tech to doom 3 tech is somewhat like comparing the half life engine with quake 3 (albeit less-so in this case), they can both create decent looking stuff but the quake 3 is still going to blow whatever the HL engine can do out of the water. Of course this is not taking into account some of the other features of the two engines, which as I said makes Unreal as it stands able to compete with doom 3.
Wait until next year when we see hard facts and media of the UW engine, I think it will be giving doom 3 a run for its money.
But if we must compare, I would say that the Unreal engine is inferior, yet it will appear superior due to the user support, the artists behind the games and the experience the developers have, and of course the outdoor stuff.