I had thought that this was one of my favourites, so I had been looking forward to curling up with it again.
I was disappointed. Carlyon is a shadow - a two-dimensional placeholder. He has a certain Avon-ish omnipotence/omniscience but without the character.
Elinor is fine, but again not a patch on her successors eg Abby Wendover, Ancilla Trent, etc. For an experienced governess she seems incapable of initiative, being rather feebly directed by Carlyon, Miss Beccles and even the Hon Nicky in turn.
The lost letter plot is a bit Talisman Ring, and oh how we cringed last time. This is better, but the convenient deaths are tedious, and far too much happens offstage, so to speak. GH "tells" us too much, instead of "showing". Poor.
Bouncer is a mitigating factor, of course. I love his guarding Elinor where she has to be brought food and drink and things to do. Also Nicky's disdain for Francis who prefers cats... 
Any other saving graces? I wait to be convinced.