Here are some:
Raiding for resources (mana, gold) is problem. People do not care about losing a few HB over lost raid. So they are willing to go for Gold/Mana Vault even if they cannot win (get over 50%) and it’s impossible to pack all your Vaults within your walls.
I think that this is wrong. Defender has no profit from such an attack, not even shield and can lose significant amount of this resources.
Solution: To raise amount of HB that somebody lose over lost raid. Or reduce amount of gained resources if the attack was not successful.
Or maybe reward for successful defense would help.
Guild chat is tragic. No offline history at all, bad rolling if you miss something due to dungeons or HBM. A lot of work here to be done.
Troops Hiring. You can remove your heroes from heroes base, but you can't do the same for troops. Why? It would be useful to remove them (if you want to do HBM without troops) and simply put them back afterwards without waiting for re-hire.
Edited 2014-07-09, based on comments
Heroes Trial needs to be improved. "the rewards are quite insufficient for something that takes 6 hours to load, and is quite challenging in later levels for the majority of the Castle Clash players"
Edit Mode is step forward, but it seems that not good enough.
- "I find it almost impossible to just put a row of walls down without missing a few, and then having to put them somewhere else and drag them back in"
- "What purpose serves edit mode memory if it's not long term memory and designs are overwritten?"