Like many, C³, is a lightly couple series of short arcs that meant to be for both character development and tie-ins for the final battle. While this is a very typical in recent anime trends, C³ added some extra dimension such as twisted people with twisted mind as well as some pretty graphical scenes that you wouldn't normally expect from the show after seeing the earlier episodes.
As a whole, I think it's one of the better series of the season. It achieved a good balance between what you would expect out of a typical series as well as a couple of surprise factors. Although from time to time, they drop in a big dose of fan service, it managed not to cross the line of excessiveness.
Recommendation: I think this series is not very well received by many, citing mediocrity in execution and plot distraction being the major disappointments. However, if you put the series into the context of light novel, which the originally was, those two problems would be irrelevant since they're seldom used to measure the quality of light novels. So in my opinion, as long as you've set you view correctly, this is actually quite an enjoyable series. Though not as a much watch recommendation, it's definitely amongst the better ones came out in October 2011 season.