Fun and solid game. The trick to the game is simple: do the math before you start moving on the level. Also, much of it is backtracking after powering up a bit. For example, once your defense makes you take zero damage, go back and collect money by killing weak monsters. While I'm on the topic of powering up, don't buy upgrades till the second altar (at least). It's much easier to wait before buying so that better upgrades are cheap. Final hint, watch for hidden passages on the walls.