Man, I love Hibari. I've never played that game but from what I can gather about her she seems like the most entertaining form of brutal giant girl murder.
I agree with you about Hibari, she's pretty fucking awesome Unfortunately I don't know whether there is any reason to buy the games besides Hibari (I heard its pretty average in terms of quality)
And what does that mean besides fanservice (which is nice and all, but is the combat any good? Is the storyline any good? Are the characters interesting at all? Will it last a while/is it replayable?)