I like both for different reasons. I like Blooming because it ties into the story but I don't think they explained what it is as well as they could. It's a good story element but it feels like they didn't know what it was either. However I dislike it because it doesn't do anything other than give the ghosts more attack power. And because it's so easy to fight the ghosts in 4
and beat them with type 7 film because the game has no challenge to offer other than the Kanade fight they never have a chance to attack with their new power so it feels like a huge waste. Also Blooming rarely happens. I can go an entire playthrough of 4 without having a ghost bloom and I have no idea what causes them to do so therefore it feels pointless. I do like the effect on their faces though.
Dark Returns while not being tied into the story
because they had no interest to make more story other than the twins which while great additions is upsetting I feel work better than Blooming because they not only make the ghosts more powerful but they gain new attacks along with the new attacks they already were granted when in their normal forms. They also get more health which can make the fights more tense. I can see where people are coming from when they say that it makes things drawn out and it definitely does in the case of Mr. Kiryu how you managed to make that fight more boring is a feat only they could accomplish and Ryokan, but I think for the other ghosts it works really well and is a great gameplay addition that does manage to scare me sometimes especially with Broken Neck Woman and Sunken Woman.
I'd like for it to return in future games so long as it builds upon how it is in Deep Crimson Butterfly just as Deep Crimson Butterfly built on how it was in 4. However I would prefer it to be tied into the story again like in 4 but this time fully fleshed out.