The only poor review I've seen of the C4 is by plummet who goes on and on and on and on and on and on about how he doesn't like it for freeride any more.
I'm actually with the stupid - my first C4-s were 2010-s, which were honest freeride/do-it-all kites. Then i've got 2011 which was already changing into something else - 15m was a huge disappointment as it was sitting a lot deeper in the window when the 2010 and had considerably more bar pressure, 12m was sweet though... After testing some 2012s it became clear that Ozone is working really hard (and rather successfully) at turning C4 into RPM and after trying other kites from other companies I've unloaded all my C4-s for good as I have zero interest in all that wake-mambo-jumbo.
That being said - you have to decide what do you want from a kite. If you're a hardcore waker - can't go wrong with either. But if you're an average Joe looking for a "general-purpose"-kite, you might want to look elsewhere.