I love SvZ from version 1 to what it is now. But I'd like to suggest some things to make this game really awesome.
1/ Every game will become boring after long time of playing till the very end. But if you add another mode name "Survival Mode" to make anyone test how long he/she can suvival in this game is really great. It shoud count for time, not for point.
2/ Daily challenge, artifacts wave and official wave should add more different waves to test player's skills such as defend, attack, the combination among these allies, charms and how to fit them best to win, also right hero to play. Daily Challenge shoud have about 30 different types of wave.
3/ All friends of mine said: After using coin to upgrade all things to a level need gems to upgrade more... So, why do we need more coin in Daily Reward? This seem a little meaner than SvZ version 1 at which we have different type of rewards each day. From this, I suggest you add day1: 500 coins, day2: wealth charm, day3: lucky charm, day4: revive, day5: 5 gems
These things will make people long for playing tirelessly.
4/ SvZ 2 does't have Pachinko as version 1. I understand but as which mention aboved, with the redundancy of coin, you should add "a machine" which help convert coins to gems. I understand this game is free and gems is the only way to help you get income. However, you should be more generous, I make sure more and more people will please to buy things such as gems, 2 other heroes, champions, etc at any cost they could afford
5/ The fearest boss in SvZ 2 is the CRASH. Many time, i got mad when i was about to win with many reward, then it CRASHes out and I lose everything... A manual resolution shoud be add to help player with low system. Take Iphone 3GS or Ipod touch 4 (which doesn't has a strong RAM as iphone 4 up) for instance, this game is too heavy to run properly, without lag and CRASH. You shoud add Low, Medium and High *Resolution to this game. Ex: Low Resolution will not have the animated fire, sakura falling, smoke, thunder, blood, etc. To help this game run smoothly.
6/ Multiplayer through bluetooth, wifi connection.*As other great game allow players compete to each other directly, take Asphalt 7 for example. SvZ should have a mode for 2 players directly FIGHT EACH OTHER, also this mode should make 2 players FIGHT TOGETHER when a player get stuck and need help by his friend. If it could be true. SvZ will be really fantastic.*
That is all what I can suggest now, hope it is useful enough to you. Again, thank all of you for making this interesting game