I agree that many point-and-click adventures have this one moment where you either need to do something completely crazy or pixel-hunt some item you need, but don't let it turn you away, because the rest of the game is great. Usually it's solved randomly after a few days of frustration, or peeking into some FAQ to save the nerves.

From the games available on GOG, and focusing on less obvious choices, I would recommend The Last Express, as it really is something else within the genre. Gabriel Knight and Phantasmagoria are good thrillers too.

For a hilarious adventure you may want to check out Simon the Sorcerer series.

Outside of GOG, and I have no clue how you would get your hands on them right now legally (I hope they eventually do come here):

Serious:
Blade Runner
Dark Seed 1-2
The Orion Conspiracy: Trust No One (svga version)

Fun:
The Legend of Kyrandia series (part 3 is especially funny)
Innocent Until Caught series

Sorry if stating the obvious, but I tried to focus on the games that wouldn't spring to mind immediately but still worth a look if you like adventures.

Yeah, I believe MI1 was the first game they made where it was nearly impossible to die and impossible to get stuck. Maniac Mansion, Zak McKraken and Last Crusade all have a lot of deaths and dead ends.
My favourite 'death' in Monkey Island: http://www.youtube.com/watch?v=n9zUYfomAag

[rantish]
Exactly, certain mixes of characters could render Maniac Mansion 'deadended' from the very beginning, without the player ever knowing what was wrong. Thing is, people like to bash Sierra games, without seeing that early LA games suffered from similar issues. Sierra games had a completely different approach to the matter, death and deadends were a natural way for the player to learn about the environment, while LA's policy was completely different. So, it's kinda interesting that a design element of one game is a design flaw of the other, even in the same genre.
TL'DR: Deaths [and to a certain point deadends] were not a bad thing in adventure games. To a certain point they actually expanded the game.
[/rantish]

Yeah, that's a nice little tribute there. ;)

I'm 99.9% sure you can finish MM with any set of kids.

I'm not sure about the kids, but if I recall correctly, in MM you can screw up by pouring the paint remover into the pot plant or something like this. Of course it's a stupid thing to do, but you don't get any hints that you just screwed up your chances to complete the game, even though you can continue playing.

I was pretty sure the game had that issue, then again, i might've read dumb reviews, as i myself never tried all combinations. I'm pretty sure the game had quite a few dead ends, both from missing or misusing a certain object.

Point is, or was, that the issues mentioned in the OP are not only not Sierra restricted, but also, not very Sierraish to begin. with. The whole oversaturation and demonization of the issues in Sierra games is irritating.
Problem 1 is frequent in amateur productions and adventures of less known studios, same with problem 2, it's sadly an inseparable element of those games. While problem 3 is by far an issue of the later fpp adventure games which incorporate more and more logical puzzles to the mix.
So when someone says stuff like 'it must've been Sierra' it sets me off. :>

Sorry for derailing.

Dave and Jeff are the only kids who do not have a way to beat the game. Since a team is 3 people it's always possible unless you completely mess up somehow (kill off the 3rd kid say) otherwise theres a way to complete the game aslong as that 3rd kid lives (and the person with the front door key isn't locked in the cell with the others locked outside (now that really is an edge condition))