I was really drawn into it at first. There are a number of unique enemies that take different strategies to defeat, and the shooting/defense combo keeps you engaged. However, I ragequit after losing the sixth level four times in a row.
First, the arrows eat up way too much of the available weapon upgrades. Once you get past the first few levels, the arrows really aren't that helpful compared to other weapons - especially the cannon. Despite covering the board in fully/mostly upgraded traps, a lot of the faster creatures got to my castle before I could kill them. The cannon is the only main weapon with enough damage to make it worthwhile on stronger enemies, but it shoots too slowly to be truly effective. The reverse is true for the bow and for the shotgun - they shoot more quickly, but deal far too little damage for fending off hordes. On level six, the swarm of explosive blobs destroyed my castle in a matter of moments despite having fully upgraded the bow, shotgun, and cannon (plus traps).
That said, I didn't really explore the magic elements of the game at all. Maybe that would have made a difference, but like to think that's more of a possible path to victory itself than a supplement to the normal weapons.