Woo...I finally got to see the Animatrix DVD yesterday. Totally jawsome stuff. I'm sure there will be spoilers in my impressions, so read at your own risk.
Of course I enjoyed The Second Renaissance...I think I may have been the only person happy to see the humans get their comuppance for their mistreatment of the robots, though

I really liked the allusions to moments in our own (human) history put upon the robots. Having hundreds of robot "slaves" building a pyramid-shaped building a la the Egyptians, the "war footage" of an android being shot execution-style just like that infamous Vietnam newsreel video. And the solitay robot standing in front of the tank to hold it back from attack his city (like the raid on Tienemen Square in China). I wonder if, on the scene in the UN building on part 2, the humans actually signed their flesh away in that treaty...like they (the world government) willingly signed humanity over to be batteries for the robots rather than face extinction? Maybe it was a ruse by the AI, but robots don't seem the kind to play tricks...they are too logical. Anyways I thought the part where he signed his name in bar-code form was totally sweet.
My other favorites were Beyond, A Detective Story, and World Record. I really liked the character designs on Beyond and World Record, and I totally dug the retro-future style on A Detective Story.
What I like most about the whole collection is that they fall perfectly within the world of The Matrix, and you can totally believe that these are just snapshots of events that happen in that universe. I hope that this isn't the last of this type of project, because I'm sure there are many other animation directors who would jump at the chance to create their own chapter in the Matrix saga.