I cannot recall a game with a mechanic so infuriating as these bat clouds. They absolutely steal from any means of getting passed the third tier because they simply reduce any vertical momentum you may have. I find myself literally gritting my teeth every time the animation appears. I spent an hour trying to get to the first box over the ocean, and changed the point allocation for the critter repeatedly (not noticing any effect for more or less bat upgrades). I don't normally like writing only negative comments, but because of this one thing I've had %1000 less awesome playing this game than any other Berserk game I've played. Because those are all pretty much great.
I think this is a potentially great game. I say potentially because there are a few things I think are wroth tweaking that would probably bring this up to a 5 star game for me. I see a lot of complaints about both healing and replayability, and I stand by those as well. I generally end up playing with all my characters near-death and reviving one another, simply because healing potions seem to have little merit unless you stockpile them for bosses. Also, after a dungeon crawl, it would be nice to at least be able to import a finished character to a second or third slot on the party menu, so that it's almost like you have some vestige of non-random customization. I can appreciate you wanted to go for a fast dungeon-delving game, and I actually don't know if a full storyline is even necessary, but there are certainly some fun-killing issues that could easily be addressed.