It really is difficult to be impressed when it's the fourth iteration of the same game that was made eight years ago. Aside from graphics, each incarnation of UT has brought little new to the table.
I don't know. After I played Half-Life 2 Deathmatch, I got really spoiled on the physics engine. Being able to manipulate and use the environment to your advantage is immensely satisfying. Gears of War was pretty, make no mistake, but it was also completely static. Look, but don't touch. I can't imagine UT3 being any different since it probably uses the same physics implementation.
Another thing I've come to like about HL2DM is the distinction between walking and running. In UT and Quake, you are always running and there is little reason to ever walk. In HL2DM, you walk by default (granted, it's a fast walk) and can sprint short distances. What this provides is an added dimension of movement on a 2D plane, which is vital because HL2DM's environments tend to be realistic and flat. UT has, for years, tried to compensate with insanely overcomplicated, multi-tiered maps with corridors and passages that are comparable to Descent-on-foot. The homebrew level community has taken this to ridiculous lengths.
Myself, I prefer simple-stupid deathmatch layouts with at most two tiers.
