I've only watched the most recent and oldest films on the list (about 35/100), as I'm only in the '40s of my
http://www.movieforums.com/community/showthread.php?t=36034, but I do have some thoughts.
Snow White and
King Kong may "deserve" a place as influential and ground-breaking movies, but neither are good to watch. Basically everything about them sucks (acting, pacing, script, story, cinematography, and you can see this even comparing them to other films of that time) apart from the innovative animation features in each.
The Philadelphia Story is good, but there is not enough to put it above The Lady Eve, Pygmalion, His Girl Friday, and other similar rom-coms of the time, and in fact it's script is less witty than any of those and is even quite boring at times. It does have a larger cast which makes for interesting relationships, and the story is less ridiculous, but overall not as entertaining.
Intolerance. Not as good as The Birth of a Nation. Actually, both films were great, but I feel Birth was left out for moral reasons. Zero surprise when I looked up the original 100 to find Intolerance missing, so it was clearly thrown in as a more politically correct alternative to Birth, which was removed. I think there is a reason that until now it was Birth given the honours. Still not too upset. Birth is more coherent and ground-breaking, but Intolerance is more ambitious and impressive.
Duck Soup. The Marx Brothers just aren't funny. In fairness, this is their least terrible one I have seen, way better than
A Night at the Opera... which is also there! The only scene I remember from that one is Chico playing the harp on the boat. I think everything on either side of that scene was dire.
Bringing Up Baby. Very mediocre. Other, earlier screwball comedies such as The Thin Man, My Man Godfrey and The Awful Truth did far more for me. No idea what Bringing Up Baby did that was special, except star two high profile actors.