I haven't managed to beat any bosses yet, but then I just started playing a couple hours ago. But it's pretty engrossing. I mean, when something's challenging, and you find yourself actually leaning in the direction you're trying to go, and channeling Shini's capacity for shouting "Oh God!" a lot, that's kind of a mark of quality, I think. Plus the BGM is pretty spiffy.
A neat thing: You actually have two characters that you can switch between using the start button, like switching weapons and selecting mushroom tanks. Which are basically E-tanks. Apparently witches really dig mushrooms. Anyway, this character swapping effectively doubles your lifebar, and gives you different offensive options for different situations. Character one is basically Mega Man, but character two, instead of shooting magical "bullets," shoots a constant stream of energy that deals noticeably less damage per hit, but sometimes the extra pressure of a constant stream of damage is nice, especially when the screen is full of things that want to kill you, as it often is.
So yea. It's a neat thing I found. I thought maybe someone might be interested.
Edit: Finally beat my first boss! It turns out the "two characters" thing adds yet another facet to gameplay: boss powers aren't shared. When you've laid the smack down, the boss drops some manner of thing that you can grab for REAL ULTIMATE POWER, so you don't have to worry about actually finishing off a boss with a specific one of the two characters for her to get the power. Anyway, since I've only beaten one boss, I can't say wether or not the powers are actually different depending on who has it, but it's certainly a possibility. <p><div style="text-align:center">