The way towers prioritize enemies is so bad it's pretty much gamebreaking. It should focus on Whatever enemy is farthest along with gem holders being the priority, and it should refocus EVERY SHOT. Not only when their current target leaves their range/dies. It forces towers to attack some completely pointless (at the moment) enemy while another just runs a gem straight past their line of site completely untouched. That, combined with the loss of the crypts' shots retargeting mid-flight if their target dies works to make this game awful in just the first few levels.
Perhaps a better solution than simply adding more levels to the game would be to add a feature similar to the one in Monster Slayers, but with levels. Make it so that players can design their own levels and post them on Kongregate for others to play. That way there's always something more to play, not just the same stuff over and over.
 "Cursed Treasure 2"){kind=icon}
 "Cursed Treasure: Level Pack!"){kind=icon}