The best C'Thun decks are really regular decks that splash in a few of the strongest C'Thun cards and use him as a late game power play. So Control Warrior C'Thun seems ok (only putting in like 4-5 different cards), C'Thun Druid is probably fine (be curious what your deck looks like Column).
I've only messed with C'Thun War and Evolve Shaman so far last night. I couldn't get a good list going in Evolve, I think I was going too aggro and it needs to be more mid-range. My War'Thun deck did great even if I was using more C'Thun buffers than most of the "good" decks (had the 2 drops, one of the Elders + the 2 Disciples, and one of the taunters because only opened one so far). I had Brann in there too because damn near every minion had battlecry but never did anything really cool with it.
I theorycrafted a bunch of other decks to try out. Need to get the 7-win quest done and then can see if I need to open more packs.
Edit: I did see a weird amount of normal decks last night, 3 Zoolocks and a dragon priest out of 8 games I think.