This game has a lot of potential. I've been playing for a while under the name belobog and continue to make top 10 on the high scores.
Things that need to be changed or improved:
There isn't enough to do. With only two events once you finish the story it gets rather boring if you play non-stop for a long period of time. Suggestion: make three new events where you can earn new units only(no gems to keep it balanced), but make each of the events require something to play. Like make one lets say “champions guild” only playable if you are currently in the top 20. Make another “catacombs” only playable if you made rank 200 or higher for that week. And then make another one “bad lands” only playable if you completed 25 matches on king of the hill for that week. This will encourage players to play all parts of the game while having something to do. Make these events bi-daily so once every 2-3 days.
Most cities aren't being used at all and cannot be used in a competitive fashion. Make new units to balance these cities out and make them a viable option. Possibly making the events I mentioned give special random units only winnable in those events, or making powerful units with city restrictions so they can only be used in that city.
There should be no reason to earn 2 gems for earning an achievement. Make it so you can't earn less then 12 for an achievement. This will put a lot of people off and they will quit your game in frustration.
Your goal should be retention and word of mouth advertisement “oh wow I played this awesome game” not “screw that game how can you play that”?
Replace the chat box with an irc.
New, exciting, and longer story lines. The story mode in my opinion is garbage.
To keep variety, let a new player pick his starter deck so it doesn't necessarily have to be a gold base in the beginning.
If you make even 3/4ths of these changes it will be a really solid game worthy of getting my friends into.