Games are about constrained freedom. Freedom to move and to act, but within a constrained environment that sets a problem that needs to be solved. This balance is the key to good game design. Adventure games generally block any progress within the game until you find the right key. This also happens in "Doom", but because of Doom's simpler mechanics, the algorithm to find a key is generally simpler (kill monsters, try corridors where you never been before). In order to find a key in an adventure game, many strategies are possible (to pixel-hunt for a secret object, to combine alternative objects, to discuss with different characters, to solve other puzzles).
In my opinion, adventure games will know a come-back in the future, but only after certain structural changes. The main goal should not be to find the correct "ending(s)" as envisioned by the author, nor the "right" narrative path. Adventure games should not focus on the plot, but rather on the mechanics of the plot. Adventure games should be story generators, where the pleasure is not find out what would happen in a story if we play around with certain actions or characters. Until now, most story generators have focused on creating "enjoyable" stories with Aristotle's seal of approval. The goal would be to discover what would make Hamlet avenge his father or what would make him run into exile. The actual outcome is not as relevant as understanding the behavioral rules behind the character (even if these rules are not deterministic). Simulation is a game of mirrors that let us take a peek into the mechanics of the character or sequence of actions as "programmed" by the author. The pleasure of simulation is in experimentation, not on watching a predetermined sequence of events. Future adventure games need a good setting and good characters, but not a plot. If there is a plot, it would be there just to be deconstructed and to serve as background reference. A good simulation-adventure would not be based on finding out whodunnit but in playing with the elements to frame the buttler (the store clerk or the detective) and see if we can get away with it. The real adventure is in experimentation. Think of videogames not as narrative but as a storyteller's lab.