I personalny love chalenging tower defense games and this is the best game so far. At first it may seem easy but after windpass...it just gets way harder.
Hard?Imo (campaign) was rather easy.In only 1 level 2 enemies escaped when 1st beating it!But challenge missions, they are hard, but its nice when you finally beat them, like I did
Hard... on easy mode its... easy^^ Normal... isnt very hard too, only the challenge missions (normal) was a lil bit harder, but whit the upgrades its not too hard to handle.
Think they got the level of challenge just right, had to come up with a different strategy each level although most involved a Big Bertha tower or two.