I miss not being able to plant on the roof. It took a fair amount of work to get up there - I had to build a level 3 sentry in order to get the teleporter up there, and even then, the teleporter was very exposed until you could get it moved back. (Some could plant with a dispenser, but I never figured it out) Then... you had to start building. A rocket from the canyon or nutz with his stickies made it really hard to keep those things alive at point two. That said, unless you went in smart - it could be really hard to get a turtled opponent off the roof.
Also liked building on the ledge around the point on point 2. Odd to see that removed, as that was an easy take down.
Like the bigger metal packs scattered about. The ladders are a nice touch, rather than the jumping gymnastics you had to do.
Having spawn points closed is a nice touch. Nice to not have to worry about a demo or spy popping out at point 3 spawn... course, half of the fun was nuking the person.