I quite like it. There are one or two areas where they've kept a bit too much of the old structure even for me - the hummingbird separation cages look a bit tatty, but overall it's quite a nice building - certainly much nicer than before, with much more light. It does suffer from the same problem of species repetition that always seem to affect London's bird collection, but otherwise it's quite effective. Something in the layout bugs me slightly, but I'm not sure how I'd have done it differently given the same brief.
I love this building. I like the way it looks quite Victorian and "vintage" if you will, but I also like the walk trough bit which mixes the old with the new. Great