Survival mode is way too easy. I played it for 45 minutes with 0 power ups and got over 20 million points without losing a single life. It doesn't gets harder over time. I literally had to let the zombies win or I would have been blasting away for the rest of my life. Great game, though.
Cool game. Another thing that would be sweet (that I haven't seen already listed) would be to combine weapons with different capabilities or upgradable weapons. This would allow the player to spend some of those mana pearls we're mysteriously saving.
Because the game is only 30% done :P