Wish you could increase stats by gaining levels and getting stat points. You could spend them on Strength (how much damage basic weapon attacks do), Vitality (increases overall total health), Focus (how quickly you get your ultimate), Magica (increases how much damage each spell does), and Charisma (you get discount off items in shops for how high this is).
It would be good if Premium Members could get more benefits, like an extra upgrade on every tower or something like that. At the moment I feel Premium needs adding to, also it would be good if you could find secret places on maps which gives you extra gold (something along those lines). A couple more things: Speed-Up Button, move the restart button away from "Continue" (being picky) and more maps :D. 5/5 anyways, best Tower Defence around.
I bought the expansion pack but I feel the two maps we are given are a little bit too challenging, it is very hard to get started and usually lose stars very early.
 "New Star Soccer"){kind=icon}
 "Contract Wars"){kind=icon}
 "TDP4 Team Battle"){kind=icon}
 "Card Monsters"){kind=icon}
 "Takeover"){kind=icon}
 "Siegius Arena"){kind=icon}
 "Smashmuck Champions"){kind=icon}
 "Nuclear Plant"){kind=icon}
 "Kingdom Rush"){kind=icon}
 "W-Zone"){kind=icon}
 "Paladog"){kind=icon}
 "Combat Extreme"){kind=icon}
 "Block Miner"){kind=icon}
 "Mardi Gras Mayhem"){kind=icon}
 "Realm of the Mad God"){kind=icon}
 "Learn to Fly 2"){kind=icon}
 "Hordes of Hordes"){kind=icon}