Frankly, this is just a story for Hitsugaya fans. There's even room for Ichigo bankai fans. I personally AM a Hitsugaya fan, so this is still a pretty good movie for me.
Beyond Hitsugaya's illuminating presence, however, I found that the story was lacking in numerous ways. When you find out what's really going on, the plot seems very contrived (the council or whatever makes a decision and then abruptly changes that decision without any explanation of why, which is pretty important in my opinion - why was Hitsugaya chosen? What made him better than Hisaka?). Characterization doesn't make much sense. Hitsugaya is also...randomly possessed? Wounded? What? (These were my thoughts through most of the story. By the way - Hitsugaya angst fans, this movie is DEFINITELY for you). They also start a sort of dissection of Hitsugaya's personality (Kisuke, Ichigo and Co.) and then just stop. It's really just RANDOMLY thrown in there.
Also, this movie seems to be mainly a "cameo" movie. Characters like Kisuke, Orihime, Chad, and Uryu all show up (I can't remember if Yoruichi or the store people show up, but there's a likelihood they're in there). Almost ALL of the Soul Reapers show up. And watch for no apparent reason. This is formulaic for OVAs, which are typically filler between manga publication, but it's extra silly in this movie's case. At least in the "Sailor Moon" films, for instance, the cameo senshi mattered.
I think my biggest beef with this movie is the plot holes. The main plot (the fact that there are two Hyorinmaru's) is never explained. Really. I mean, you could INFER that Hisaka and Hitsugaya have similar souls or personalities or something, which is why they're friends and why Hitsugaya is angsting so much (because it's hard for him to hurt his friend or because he could have been in Hisaka's place, etc.). But you really have to be thinking about it infer that. There aren't any noble words/sentiments given to imply that. Otherwise, the story reminds me of "Ponyo", where you're just dropped into half-formed plot. Their explanation is that sometimes there are two Zanpakuto that are the same. That's it. An explanation requires an explanans and an explanandum. WHERE ARE THE EXPLANANS HERE? There's no actual explanation - they just state the fact that it happens, done and done. So you're thinking: "Okay...well...wait...what? Why? When? How?"
Also, there's a point where one of the characters actually BRINGS up a BIG plot hole - why is Hitsugaya being accused of treason so soon? What did he do wrong? Why are all the captains and such being sent out after him? I guess this could be a possible nod to the premise of the first real "Bleach" arc: Rukia's incarceration and execution, which WAS considered over the top and no one really objected to it, which was weird (Aizen at least comments on all of this and it's explained). But of course, the problem in the movie is COMPLETELY ignored and they pushed right on.
If all you want is a reason to see a bunch of soul reapers fight each other AND some arrancars (it actually ties in, I looked up; but their presence is still kind of random, in my opinion) then this is a movie for you. If you just want to see something "Bleach" related (and you want a cameo of your favorite "Bleach" character), then this is for you. If you didn't like "Ponyo", don't watch this. It's a weird relation, I know, but if you didn't like the movie then you'd probably understand.
