Oh boy, this was a doosy. Well, to begin, this game was alright, but it has a couple of things that irked me a lot. For one, The level design was kinda basic, and left little to the imagination beyond block slopes, set up traps near said slopes. To be fair, the game itself is pretty simple, so going overboard on level design probably wouldn't have done a large amount of good in its favor. Another problem is that the levels get pretty repetitive. Since you only have 4 traps that deal damage and the traps you can use on each stage are pre-determined, it's always obvious exactly how one should complete a stage and what traps one should focus on. The main problem I had with this game is how traps would destroy one another. It makes sense for the chain ball, but it's always annoying to drop a bomb only to have it destroy my own spikes. It also makes defending your walls more difficult because spikes will break if dropped too close to those as well. There wasn't a whole lot that was done in the realms of 'innovative' aside from the story (which was a little lackluster, even if I haven't seen something like this before), it works for what it is.
For anyone struggling with the last level, here's my advice. Make use of all of your traps. Start with turrets (build them on the low ground near the princess), then build a wall at the slope and reinforce it with spikes. Drop bombs constantly to damage the boss and the mass of enemies that will pool at the bottom of the slope. Keep the wall alive at all costs. Focus on your traps in this order if you have extra blood: walls (only if severely damaged), spikes, bombs, turrets (they are indispensable, but costly and may leave you short of restoring your wall. Three or four should do fine).