Awesome concept

I really liked the change in concept from the standard side-scrolling platformer, however, there are a few minor tweaks that I'd like to see.

One annoying thing was that you cant climb down ladders, this made me often have to take the long way around, especially if I accidentally start going up a ladder then decide I want to go back down. This was also annoying when trying to avoid lasers.

Another thing is that the spears go through walls. In the later levels, the spears combined with the laser made it somewhat impossible to not take a hit every now and then.

Also, maybe there could be some kind of a multiplayer mode.
One player has a a slow income to spawn monsters and build traps while the other person has to survive as usual. The traps and monsters would take some time to build before being functional though, so you cant spawn things directly on the player.
Also, in addition to the apples, money would constantly spawn throughout the map that the survivor could pick up and spend on upgrades, like increased speed, or consumable items, like a potion that stops your life from decreasing for a short time, or a potion that makes you invulnerable for a short time, or a potion for temporary max speed.
I cant think of any suitable victory conditions, maybe the survivor wins if he survives for a defined period of time and the other person wins if he manages to make the survivor die before the time limit runs out.

Overall this is a really fun game, even though it could use some more features. More monster and trap variations would be nice.