Well with KiraGirl K, I came up with an understanding of the Bankai and why it has the same name as its Shikai (Thanks to KiraGirl)
Minazuki can be written with 2 Kanji: the first translates to "Purify the Flesh": used for her Shikai which is the giant healing manta ray. A second Kanji translation is "Devour or Consume All": her Bankai
Depending on her mood (medic or psychotic Kenpachi) determines which is used...naturally using her Bankai only in Kenpachi mode.
The largest problem understanding her Bankai was because of just WHAT she was using it for. Minazuki creates a large area of a black or blood like ooze that seemed to surround both Zaraki and herself. This is a lot like Kaname Tousin's Bankai in terms of surrounding.
Then, as we saw it tore off the flesh of Zaraki and apparently even Unohana! While in a death match she could have used her Kaidou (healing Kido) to heal herself, she was powering up Zaraki, and thus was constantly healing the both of them. This explains why they went back to normal.
Basically the Bankai tears the flesh from anything it seems to touch. It also provides an extreme power boost as after her first swing, Zaraki appeared to ragdoll on the ground as his eyes were whitened out.
Nooe that helped with what I saw from her Bankai
More on topic......I REALLY hope she lived. This new Zaraki doesn't seem so much improved....and honestly it is a retarded idea to kill your Strongest shinigami (who is also your best healer) just so you can get a new strongest shinigami....
Kubo said Unohana was entering the battlefield.....was wishing that was supposed to be her destroying the enemy not being a useless sacrifice. Also she was described as Genuine Elegence....I guess he shouldn't describe her like that and then rush her only fight. Which is apparantly is truly her ONLY fight...