It's an interesting question. I was never a Hayley fan, but she was not with the group for very long. I liked Meav's voice quite a bit, second to Chloe's in fact (but Chloe is far out in front

). What I liked about Orla was the visual icon of having a harpist with the group, since the harp is such a folkloric Irish symbol.
I think the new girls, Lynn and Alex, are fine. I like Lynn's soprano voice, and Alex is a good performer. She's also very approachable and friendly in the Meet & Greets.
Actually, my biggest regret in the change in the group has less to do with the shifting of performers than the shifting of
songs. It seems that Meav brought with her many songs that are
echt-Celtic, like "Si Do Mhaimeo i," "She Moved Through the Fair," and so on, and when she departed, those songs sadly went with her. The same is probably true of Orla as well, although I generally preferred Meav's songs to Orla's.
I think it's at least possible that the unfortunate introduction of less Celtic, more pop songs has something to do with the personal musical choices of the new girls. And if that is the case, then that one specific fact makes me regret the changes in the group.
If Celtic Woman had the same mix of classical and celtic numbers as before, just now sung by the new performers, I wouldn't mind the change in soloists that much.
ADDENDUM: I keep forgetting Deirdre. I think it's because she came and went before I was aware of CW. In the one video that I've seen of her performing with CW, she seemed to fit in well enough.