I was reading AKPhilately's blog last night where he was discussing how much engraving on a stamp it takes to make it worth collecting as an engraved stamp. This is something I've thought about a lot as well, as I'm sure many of us here have done, and it is particularly relevant as I source a lot of my stamps online. Not all sellers have high resolution scans and generally I use the catalogues to guide me.
Today I received a shipment of Liechtenstein stamps from the United States which are a perfect example of the issue but which also led me to a small discovery.
Gibbons seem to always use the same order when describing stamps so all of these are listed as "recess and photo". Scott, however list in the order of magnitude, so to speak, so if they say recess and photo, it means there is more recess than photo, and vice versa. They list all these as "photo and engraved".
Anyway, here are some of the stamps that arrived and you can decide what you think, but I'll give my opinion too. All were engraved by Wolfgang Seidel who is a superb engraver but not many of these would make my favourites list.

1991 Princess Marie SG 1019, Scott 967. Designed by Hans Peter Gassner.

1991 Prince Hans Adam II SG 1020, Scott 968. Designed by Hans Peter Gassner.
The only engraving on the faces of these is the hair and his eyebrows. Almost all of the face is photo. To me, this is not really an engraved stamp though I have to concede that the small bit of recess in the hair is an improvement. Engraving has also been used to give texture to the clothing.
Next are the 1990 game birds set designed by Wolfgang Oehry, based on paintings by Benjamin Steck (1902-1981) SG 996-8, Scott 945-7.

Ring-necked Pheasant

Black Grouse

Mallard
These are much better, in my opinion, as there is a reasonable balance between the photo used to give the colours and the engraving used to give texture to the feathers, particularly on the Black Grouse and to the background. It would be interesting to see the engraved portion on its own.

Finally, we go back another year to 1989 for the 150th birth anniversary of Josef Gabriel Rheinberger (composer). SG 954, Scott 903. Although more of the stamp is photo, the most important part, the portrait is almost completely engraved to the extent that it could stand alone.
Each year, there is a little less engraving. Whether or not this is a trend that follows on other stamps, I don't know but as a pensioner who has a limited budget for his hobby. I think that in future I will look more towards the superb issues coming from the Czech Republic, Slovakia or perhaps even China.
As this is a forum rather than just a gallery, I'd be really interested to hear other collectors' opinions.