Third time I am playing trough this game and it's as much fun every time. I actually don't think the game needs a fast forward button with the pace it has.
@densch: I myself had no trouble hitting enemies with spells 250 times, just make sure to use them on groups, using ice to push enemies to create larger groups and use another spell on that group
A tip if you are stuck on rotary level 4. Solve three triangles that are between each other and then by only switching the colors around on the three you have left you can solve the puzzle.
 "Kingdom Rush Frontiers"){kind=icon}
 "Sentry Knight 2"){kind=icon}
 "This is a Work of Fiction"){kind=icon}
 "IntoSpace!"){kind=icon}
 "Diggy"){kind=icon}