Just got done beating the entire game. Great little game, can't wait for the sequel to come out, it's called "Gemcraft - Chasing Shadows". I won't spoil the ending for those who haven't finished Gemcraft - The Forgotten yet, but it's pretty neat.
The best way to get past the epic battles is to 1:get your mana pool up really high into the thousands 2:place wells all allong the path to slow him down a little bit then 3: place towers all along the path and move your gems along the predetermined path to kill him more efficantly.