After using the fan patch in my retail box collection I see it now runs perfectly with the newest DosBox, so I really have no need for this release.
So I bought Gabriel Knight 2 and Vampire the Masquerade instead.

Ah yes, forgot about that. Still, a rather underwhelming choice for "The Month of Activision" considering that these games as well as the Space Quest titles (unlike, say, Interstate 76 or GK2) made their big downloadable debut quite some time ago...

Yeah, but the Steam version is the half assed collection that was released a few years ago. While they work fine, they used the inferior versions of games, they only have the remakes of the first games and not the original ones, and the Leisure Suit Collection is missing LSL 7 and King's Quest is missing Mask of Eternity. And yeah, Mask of Eternity sucked, but it would have been nice to have the complete collection. So hopefully GOG.com can do it properly and also offer package deals that include the releases in one package for a lower price.
I already own the retail releases of the Space Quest and King's Quest compilations but I'd probably end up buying them here too if they do a better job. Can someone make a list of the versions of each game the retail/Steam collections have and the versions that the gog.com collectins use?

Good decision man. I bought Phantasmagoria and Beyond Good & Evil.

Not true. KQ6 was also released on floppy disks, as the last one in the series.
KQ7 exists also as a DOS version, it's unproblematic to get it running under DosBox.
About the games: I think KQ6 is worth to be played even today. The fourth part is nothing special and KQ5 is just abysmal, save for the graphics and music.

These games look fun, but I'm really, really bad at adventure games.
Even the Telltale games (Sam & Max, Tales of Monkey Island) are too hard for me. I end up following a walkthrough through 70% of the game.
Are these games somewhat easy? If not, are there any easy adventure games on Gog?

Just like the Space Quest games, these are going to go on my wishlist til games 1-3 are out.

I'm intrigued, but outside of Gabriel Knight, I don't have much experience with Sierra adventures, and I've heard nasty things about some of their games being unwinnable if you overlook an innocuous item early on or something like that (I know you can similarly screw yourself in GK1, but only toward the end, as I recall). How harsh are King's Quest 4-6 about that sort of thing?

Logic has never been The Quest Series'...forte, so in short I wouldn't really consider them easy. Some games on GOG I would recommend if you want some good, challenging (yet logical) puzzles would be Sanitarium, or the Tex Murphy series. I also loved Gabriel Knight, but that has a few tough puzzles. If you feel up to the challenge though, check it out.

To this day I'll never forget the use for the pie in King's Quest V. I used to play these games with friends and family, when they saw the use of the pie, everyone in the room at the same time went:"What the **** was that?Really Graham?", they burst out laughing. Its one of those try everything on everything moment in adventure games.
"Try the pie for ****'s sake"

Yep and both of them are far superior. There's also a remake of the 3rd one which is fully mouse driven. LSL2 has a fan made remake as well which is fully mouse driven, although the graphics are identical to the original.

My only wish was that GoG or someone else was working on a tool similar to DosBox for Windows 3.1, other than going through some convulted Virtual PC step. The downside for these Sierra games, including these King's Quest titles, is that stuff like improved midi music and enhanced character portraits were available but only when you ran it in Windows.
You definetely should skip these old Sierra games. I would recommend them for nostalgia fans for the most part. Not only are they way harder than the Telltale games, but you could easily screw yourself over, as they notoriously contained numorous ways for your character to die as well as dead ends. If you do play them, save constantly and using as many save slots as possible!

It's true, the KQ games are quite hard and not always fair. But the sixth part is well designed. It contains some dead ends, but sometimes you might be able to avoid them if you think ahead. There's still one you can be trapped in that can't be foreseen, but otherwise I think it's fair.
Newcomers should probably start out with some less harsh older classics, like the later LucasArts adventures, Broken Sword or Death Gate.

As a fan, I feel that KQ6 was mostly written by Jane Jensen. It does seem like Roberta managed to spoil the gem slightly.