Well, the differences between CC and COD (according to my experience in these months playing COD) would be:
1. Buildings: In COD you can find the Workshop and the Caravan.
- Workshop: you get equipment crafting blue crystal or gems with Blacksmith, you can level up that equipment (using Steel) to make stronger your heroes. The equipment give you: Attack, HP, Crit Resist, Crit, ACC, etc.
- Caravan: you can get rewards using gold, credit or gems (only once). If you level up your guild, you can get free rewards, but you need to donate shards to get them.
2. Warehouse: Similar to CC, but you can get items buying them with water (mana). This give you X karma, Which if you get 1.500 karma you will get a free roll.
3. Heroes: The difference is the appearance, that is, they have an oriental style. Here we have, what would be in CC, until Valentina.
There is a New Hero that does not come in CC, and he is Abjurer. You can get him buying opals.
As the companion Smitty338 comments, Maahes (Aries), Nirgali (Vlad Dracula) and Graveshadow (Moltanica) can only get for events....well, Mahees and Nirgali can get too in Heroes trial but It's difficult (for me); and you can get Graveshadow easily because there's a free event (The Joys of Daily Login) where It give you 20 Medals, so you need five times that free event.
4. Opals: It is a new form of payment in the game. It allows you to get rare crest lvl. 3 or 1 rare Legendary Hero Card (or a Pearl xD). You only need to roll 150 opals.
5. Medals: In CC It's called like Soul Stones. Here you need 100 Medals to get 1 Hero, but in CC It's 200 SS.
6. Game Modes: They are similar to CC, but in FF (Forstress Feud) you have to fight first against a warden (which gives experience to your Heroes, then you go to FF.) In the end, the rewards are good because they give you gems.
7. Dungeons: They are easier than in CC, but they give little experience. In Expert Dungeons you will find the garrison towers till the Expert Dungeon 7.
I don't know yet the difficulty in Insane Dungeon (because I haven't arrived yet).
8. Game Events: There are many free events, just like buying gems. There may one day be no free events, but they appear very frequently. The most popular (from my point of view) are: Punch the Minotaur and Lucky You.
9. Sweep: Here, in COD, you can Sweep raids and Lost Realm. You need to buy gems so you can sweep (you need a rank VIP). This isn't important.
10. Sanctum: It's the place, which allows you to make strong your heroes for FF and also for lvl. Up your equipment (because it asks for requirements). This requires repeated Heroes to boost your Heroes (raise the score).
11. Server and switch platform: There's only 1 server (with languaje: english, arab and Türk), and you can switch your account between android and iOS.
Conclusion: I think COD is headed for f2p. It isn't necessary to spend money, unless you want.
Ps: I'm sorry if I wrote too much -_-"