What he was looking for was stated fairly precisely. I've added a few words here:
You have (a maximum of) of two minutes to draw a maze that takes me (a minimum of) of one minute to solve
The first two mazes are too easy, with a path that goes from one end of the maze to the other. He solves them very quickly. The concentric circle maze was much harder, requires more searching through the entire space to find the path through to the next layer. She even uses the notebook cover to create it, so she is not mentally constrained by the grid lines.
He doesn't care what the maze looks like, merely that she is creative enough to create a puzzle too hard enough to quickly solve quickly.
He needed someone that could create a dream environment complex enough that the projections find it too hard to easily navigate to find (and kill) the architect.
I do appreciate the fact that the circular maze looks unsolvable. I can't explain that other than this is a small mistake in the movie. I personally don't think there is more to this than the first two mazes were too easy.