I don't own a C max, but I do own a 2013 Fusion Hybrid, which has the exact same hybrid drivetrain and is very, very similar to the C max.
I can tell you our Fusion has been flawless, one of the best cars I've ever owned. I would absolutely, in a heartbeat, buy another one! Amazing fuel mileage, an absolute blast to drive, and one of the simplest and easiest vehicles to tow behind a MH. Just put it in neutral and go, basically. No disconnecting fuses or batteries, no starting and running the engine every few hours to lube the tranny, no special crazy procedure to go through when hitching it up. None of that nonsense. C max's flat towing procedures are pretty much the same as the Fusion hybrid, since they have the same drivetrain.
I've read several reviews, issues, etc. on the C max. As DouglasC already mentioned, most of the issues are related to the 'My Ford Touch' informational system. Fortunately, I did not like that system from the first time I saw it, and specifically looked for a Fusion that did NOT have it. Really glad ours doesn't. This vehicle's dashboard is complicated enough without that, haha. :)
As to the mileage: I laugh every time I read various reviews and other things, complaining about how Ford hybrids don't achieve the mileage that Ford claims. I personally, have not achieved Fords claimed mileage very often, either. Nope, instead, I usually BEAT what Ford claims! In everyday commuting to work and back (26 miles, 'bout 80% highway), I'm averaging between 48 and 50 mpg.
I will say this: Hybrid mileage is drastically affected by driving style, more so than a conventional drivetrain. If you drive like a 'leadfoot', and must be the first away from every stoplight and the last to start braking, you will never see the rated 47 mpg. OTOH, if you go easy on it, and try to keep it in EV mode as much as possible, you will easily see 47 mpg or better. Best I've ever seen was 53 (average), on the way to work.
Also, hybrids will not achieve as good mileage in the winter, like already noted (cabin heater forces gas engine to come on more). Long interstate trips where you run at 65 mph or higher nonstop will also bring the mileage down some, as at those higher speeds it can't run in EV mode as much. Still, though, even on bitter cold days or on long highway trips, I can still easily average 44 mpg. This is much, much better than any comparable vehicle with a conventional drivetrain will give you.
Be the mileage what it is, we really didn't buy it for fuel milage, that was just an added bonus. We spent the extra $$ for a hybrid, mostly because of how much simpler it makes flat towing behind the MH.
Only thing I don't like (and this is very minor), at least related to the Fusion hybrid: Trunk space is a little lacking, due to the large batteries back there I'm not sure, though, if that'd affect the C max hatchback design quite as much?
Bottom line: Go check out and test drive a C max, or maybe a Fusion hybrid. If you like it, and can negotiate a deal on it within your budget, go for it!! You will not be sorry.