I've played another game like this and in that one they did this great thing that the elements you can combine with something at the moment have a black frame, those that had no more possible matches ever had a grey frame and those that you just couldn't combine with something at the moment had a dotted frame. I really liked that. Otherwise I've always loved these games.
My biggest problem with this game is that the towers are far too expensive it just makes it really really hard to beat the game even at the earlier levels
I find it quite annoying that sometimes the game won't load at all. I just get the first screen and that's it. I understand that you might be updating or something but if you are let us know. Or it might be just me it doesn't always load for.