Great Game!
There's a lot about this game to like, for me, because I totally dig puzzle games like this one. The mix of roleplaying elements with the puzzle game and the "Gauntlet Legacy" styled shop system kept things original. Awesome concept, music made for zoning out on.
Though I gave full NG rating, I do have a couple minor gripes about this game.
1. Standard Game Play Mode - As people have pointed out, the Devil's a godawful fight. Resource management (shop stuff) is so insanely critical at this point, that you can end up going into the fight blind, and probably without anywhere near enough stuff or health. I managed to tag him four times with a lucky Heal Vial spawn, but that's just not enough, given the limited time he gives you before slapping you down. This basically means if you start off bad, you're SOL and have to start the game from scratch. I don't think shop should be necessary, but how about a full heal before the fight?
2. Purgatory Mode - Insanely repetitive. Once you get the cycle down, it's just a matter of resource management and you can pretty much go on forever. I think I managed to pull off somewhere around level 30 at around the 200th arena, and I still haven't been forced into a stopping point. This is probably because the game doesn't get harder, it just cycles top-to-bottom from weakest to hardest critters every 50(?) levels. This turns it into literal purgatory, grinding out the EXP to hit the #1 rank. It felt like an achievement the first time, but.... y'know?
3. Spruce up the Storymode Map! Compared to the rest of the game, it ends up looking kinda shabby.
Otherwise, the challenges are good, and I still haven't gotten around to completing them all yet. Perhaps get the Medals feature here? :)
