Personally, I've only seen a few of the anime episodes but I read the manga voraciously. The manga is nothing short of GREAT, I love it!! But still there are points that can be discussed.
Let me say now that I've got all of them up to volume 6, and volume 7 comes out next week, so if your tender eyes want to avoid spoilers then LEAVE. NOW. And it'd be nice if that could hold for the entire thread too, so please don't include spoiler warnings in your responses.
Otherwise, on with the show!
First thing I think needs discussion is in volume 5. Celcia breaks free of Dawn, but how?? I didn't get that part at all, it felt too much like a deus ex machina, but if anyone else has a different bead on it I'd love to hear.
Second thing, WTF is with the first episode of this series in anime??? It felt like the animation company had some stuff left over from a previous show that fell through and they just thought, what the hell, we'll use this anthropomorphic sea animal fighting stuff for the first half of this series! Even though it's got NOTHING to do with the manga! If I hadn't had another episode or two to watch after that I would have written the show off as abominally stupid and moved on.

Finally, Mike just rocks, who wouldn't want their own self aware tank!?!