What's NOT to like is the fact that it fails to make sense, it fails to move me in any way, it doesn't have any real high points (such as the ending of Ghost of Perdition). In every way it seems to be only a collection of riffs and ideas of which some are great (such as the "medieval" vocal part) but of which most are pure nonsense.
I think you need to think about the feeling of seeing it live more than about the actual song. To a lesser extent, The Grand Conjuration is the same way, it seems too repetitive to some (I love it personally, but I see where they're coming from), but you have to consider the sheer energy that ultra-heavy song can pump into a crowd with its "THEEEEEEEE GRAAAAAAND COOOOOONJUUUUUURRRRAAAAAAATIOOOOOOOON" and all. With Black Rose Immortal, I completely agree that it's disjointed and doesn't work very well as a song (all the riffs individually pwn though), but with how long Opeth has refused to play it, if they suddenly whipped it out for one leg of a tour, the crowd would probably go nuts in a way that makes Deliverance look like Hope Leaves. Also, it's almost a gimmick, but the sheer length of the song gives it a more epic sense live ("Oh ####, they just pulled out a 20 minute song")
In addition, to the "no real high points" comment, that extended scream around the 19 minute mark is sort of a climax to me. As far as the issue of disjointedness goes, Opeth has demonstrated since MAYH that they are capable of creating tiny little transitions from acoustic to distortion and vice-versa that make their songs much more coherent, and they've also made tiny little changes to the live versions of songs once in a while, so what's to stop them from just adding little moments that transition the distortion into the acoustic passages. And for the length issue, I think we can all agree they won't be playing that violin bit at least...
Overall, I don't think BRI is the best Opeth song ever or even in my top 20, but I also think it's a tad underated by all those who absolutely can't stand a bit of disjointedness.