Ennemy have way too much health, and you gain almost no money, making the bishop waves almost impossible too kill du to crappy splash tower ( seriously, 10 damage per shot for a pack of 1000 HP ennemy ? o_O even with upgrades the damages is way too low )
Training is useless. I just reach turanggamasa lvl 4, I try the Spearsman, but I just can't kill anything in training, I start lvl 2 while ennemy in training are almost lvl 4 with far more better stat ( Raptor Rider ). Having to lose 10 time just to level a bit is just frustrating and boring.