One of the biggest obstacles we've encountered so far is agreeing on how to spend our time. Level of detail is a big issue. Since we are working for only a short time on a game, we'd like to stay more or less on the 'big picture' level. However, in order to really discuss a game idea, you have to look at some of the details or else you are ignoring what makes the game unique.
At one point, we began making a spreadsheet of all the unique objects in our prototype game. The point was to be able to deduce a general nomenclature or way of speaking about how the objects interacted on the player's goals. This seemed unnecessary in a lot of ways because it meant spending a lot of time sitting around talking about what the cat 'might' do in any given situation. Since we didn't have the cat in front of us, it was rather easy to neglect certain ways in which the cat could interact with the object (it could come from behind, it could approach it diagonally, etc.) Furthermore, when we did identify a tricky situation, our solutions were primarily artificial. They were created in vitro, if you will, away from the living creature. They would not necessarily make sense in game or to the player.
This gave way to an overall sense of urgency just to 'play' and figure out what would happen from there. Play-testing was a great way to identify the gaps in our thinking. From our play-throughs, we were able to better organize our thinking. On the other hand, play-testing meant we were much more likely to get hung up on details. If we wanted to make a functional prototype, we needed to have a very narrowly defined set of rules that were consistent across all play times. This meant sacrificing a good deal of creativity and invention. We had to allocate all of our time during this period to making one singular idea work. Even though we had many different ideas of how to approach the general concept, we were forced to focus on the details of this one idea. This led to a good deal of frustration and perhaps a more narrow mindset then was appropriate for such an early stage of design.
Obviously, this can be somewhat compensated for by splitting the group and working on multiple conceptual ideas at once. However, this does not totally address the issue, since the actual prototyping stage still limits the freedom of the designer. I think the main lesson learned is that there is an overall role for both of these processes (the creative, free-flow, no-limitation of verbal analysis and the more constrained, practical approach of play testing). The important thing for the team will be to balance creativity with practicality. Similarly, we will need to be able to problem solve any major flaws in our design, while avoiding getting too caught up in the details.