What a great game! I beat 100% on normal, wave 50 on survival (what an awesome item!), and all normal challenges, now I've moved on to hard. The difficulty curve was nearly perfect, the large amount of "optional" levels on the world map let me level myself up without needing to resort to grinding too much between bosses. I found that completing levels on 100% to earn diamonds, let me craft way better items than I could get in the shop. For most of the game, my equips were nearly double what I could get for any amount of gold, because I saved up to craft only rare items that ended up giving me huge hp or attack boosts in addition to the usual effects of the item. The only boss that nearly made me ragequit so far was the final one in normal, I have a lot of trouble with the dodging so it took me about 15 tries to beat it.
Now that I've started hard mode, I find that all my stats and equips carry over, so I've been blasting through levels. The first "hard boss" took longer to explode than I did to kill it. I hope the difficulty ramps up soon, I can literally beat levels by walking away and letting my ship shoot every single creature.
A few issues: Every so often the game starts to bog down my whole computer, occasionally crashing anything I have open. I'm glad that it autosaves even if I have to close the page, otherwise I would've quit days ago. Another problem I've encountered is that the game occasionally stops responding, especially in the flame challenge. Either it will refuse to begin the battle when I click "fight," unless I refresh the page, or it will refuse to end a battle even after I've killed everything, until I click retreat and then restart the level. The only reason this doesn't make a huge impact on my rating is that I've never had to redo more than one level because of this. The music gets very repetitive, particularly in survival mode. There are several songs in the game, but only one (or maybe two?) actually play during battles. I would like a little more variety in the background music.
Other than those (minor) complaints, I found this game to be incredibly enjoyable and entertaining. Thank you for putting this on Newgrounds!