From a non-build perspective, the change in frame perimeter this year kinda made more robots look like, well robots. Teams used the space allotted a lot more efficiently and as a result many bots have a shock factor to them, the whole "I didn't expect that to come out of there!" effect. In my opinion it makes many bots more exciting to watch because they can now be seen as efficient robots meant to complete a specific task(s), as opposed to giant hulks of machines that did everything and still had space to spare. While the bigger sizes of the past had an "I don't want to get in front of that thing" aspect to them, the newer smaller sizes offer a robots working alongside humans aspect because they are less scary... minus the discs being shot at high speeds aspect.
The new size forced teams to not only design how to do a task, but how to do it as simply as possible, as there is not much room for overly complicated mechanisms. The new size also forced teams to think about accessibility for servicing. This was huge in 2010, but was kinda lost in other years when you look FRC wide.
I hope the sizes are here to stay. They are just big enough to be considered advanced machines, but just small enough to not be caged up, pun intended. Goldilocks would be happy.