Chiming in late here, so
It invariably gets compared to the Sony FS7 due to both being sub $20K cameras with the FS7 looking better on paper due to HFR and sitting at half the price. So I'll first offer some thoughts on how they compare to each other and on the C300 Mk II itself.
First, I'll start by saying that camera preferences can be a very personal thing and it often is influenced by what type of jobs you're shooting (narrative, documentary, etc.) since each job has different requirements. I've used both cameras quite a bit and while Canon's C300M2 price makes it a really tough pill to swallow, personally I always find myself fighting the FS7 and find that it gets in the way of focusing on the creative process.
For one, prior to the latest firmware, the menu system of the FS7 was just insanely laggy and frustrating to use. I also much prefer to use a joystick vs a wheel. Beyond that, often enabling one feature set disables other ones at random and gets really annoying memorizing what works with what. For example, waveform doesn't work together with the view assist LUT turned on. Plus you have to disable LUTs on all the outputs to get it to work. With the Canon C300 MkII, things just work; enabling features don't adversely affect other features.
Second, the "viewfinder" adapter for the FS7 is huge and detachable. Personally I find it a monstrosity and not a viable option. The C300's viewfinder isn't great, but it's usable in a pinch.
Sony's system of toggling ISO's between 3 presets (L/M/H) drives me crazy. If I have them set to 500, 1000, 2000 (I prefer to rate the sensor at 1000 since 2000 is noisy) but later want to rate the sensor at 4000 in a low light situation, I'll need to dig into the menu system and take 20 seconds to make the change. With the C300 MkII, I programmed it such that I spin a single wheel to change the ISO and can do so in fine increments.
Speaking of ISO, Sony's SLog3 ISO of 2000 is strange. No matter what you rate the sensor at, the image always just gets recorded at ISO 2000. This adds to the grading time to balance shots for when you rate it differently.
On that note, in SLog3, you also don't have fine grain control over the white balance at all. There's only 3 settings: 3200K, 4300K, 5500K and nothing in between or beyond. I like to get the look as close as possible in camera and not have to guess at how my colors are. With the Canon, I can dial in the precise Kelvin in 100K increments.
If you own Canon glass, you're severely disadvantaged with the FS7 because the Metabones adapter for it is extremely buggy. It's often unresponsive or will suddenly wildly overshoot what stop you want to be at. I found myself not trusting the readout for iris. As you can imagine, this makes exposure very difficult. On the flip side, if you own Canon glass, you get very impressive autofocus on the C300 MkII (with none of the bugs of course). This is a powerful solution for gimbals, interviews, etc.
Playback is a pain on the FS7. The playback button isn't clearly marked and you can't view the clips with a LUT. This is even more problematic when you're playing back clips where you rated the sensor at something other than 2000. They'll look underexposed or overexposed making it hard to judge the clip or cause concern for your client.
Other areas where the C300 MkII scores points for me in terms of usability is the battery life is amazing and you get built in ND up to 10 stops (2,4,6,8,10). I love the relay recording capability where when one card is full it'll switch to the next. Where it loses points is the tall form factor (higher center of gravity) and the separate LCD monitor & XLR ports. I wish there was a way to have those attached to the main body since the setup gets quite bulky with everything. Also, you really need a third party handle that can be easily removed via quick release (Wooden Camera, Zacuto, etc.). It's a pain to do it with the allen wrench. It would also be nice if the form factor gave more real estate to mount accessories to when rigging it up. Finally, the huge size of the battery charger is a real head scratcher.
Onto the tech specs, the color science of Canon is one of its strong points. Having a RGB444 12bit mode in 2k/HD is awesome. The bitrates are also very high across the board which means less compression artifacts. (Up to 410Mbps in 4K compared to the FS7's 240Mbps). The crop HFR on the other hand for Canon is a major downer. It's the only tech spec that it loses to the FS7. Both Sony's XQD and Canon's CFast media are very expensive at the moment.
I think the C300 MkII strikes a nice balance in that I can see it working well in both a run and gun situation and in a studio narrative environment. I could never see a RED being used for fast paced work and I feel the same way about the FS7 with all of its quirks. Other people may have different opinions. Once again, it's a very personal thing.
The big question is, is the C300 MkII worth double the price of the FS7? That really depends on what you're shooting, your own preferences, and your budget. There's no right answer. If you do both run and gun and slower paced work, the C300 MkII fulfills both roles well and in that sense it's like owning two cameras. You won't go wrong with the C300 MkII, but if you're on a tighter budget or do a lot of HFR, the FS7 is a strong contender.