Bumping the difficulty down to Easy dude to the level design, which is relatively simple to play through.
Technically fine (as in, it doesn't outbreak any rules that make it ground for rejection), but the level design is below par. While it isn't flat, it is filled with numerous empty areas where nothing happens. Enemies are mostly non-threatening and can be very easily ignored or dispatched, as if they're there to populate the level.
I highly suggest that you give your levels a major overhaul in the design department to more interesting and enaging to play. As always, I recommend this guide.