First Arcane Guardian is the hardest - after that all the others are old hat and can be taken down by creating a decent 'Mana Path' in the earlier waves, thus allowing it a first pass.
5/5 - new styles for each level is an excellent addition, as are the triple score multipliers.
Currently lvl 102 :-)
.
.
.
.
Levels 4 & 6 are hidden ones (remember these from the first game)
 "GemCraft chapter 0"){kind=icon}