It's neat, but there's only two types of towers, and one of them is way better. Ice slows down the enemies to keep them in groups, but also it's an area attack, so it synergizes with itself. Eventually you upgrade arrows to deal damage over time, but it doesn't last that long and it's only worth it on levels with few enemies. And the extra wood doesn't help for the ice towers. They don't need a large area because everything groups into the area they can hit, and they don't need permaslow because they're constantly slowing all the enemies, and it's definitely pointless after the first tower.
Thank you for your feedback! A major demo update is underway for the official Steam demo launch. I've added a new tower and buffed the Ice Tower. To incorporate more strategy and balance the game, I've also introduced a new prestige upgrade that rewards you for using different towers, along with new upgrade paths for each one.