One of the key aspects of a good survival horror game is, as you'd expect, surviving. In the original Amnesia, players were encouraged to explore the semi-open levels and scavenge both oil for the lantern and tinderboxes to light torches throughout the environment. There were a few problems with the system, namely that you would end up with a boatload of tinderboxes and never have to worry about running out, but it gave the original an atmosphere of desperation and entrapment that fit perfectly with the storyline. A Machine for Pigs on the other hand completely removes any sort of resource management; the lantern (now a torch) has infinite power, electric lighting has eliminated the need for tinderboxes and the balance created by the sanity mechanic is now gone completely. In fact, the game lacks even an inventory screen and a health system, further simplifying the game to an unnecessary degree and taking away a good chunk of the tension from the original.
Stripping out the survival mechanics has also led to the level design being compromised. There's none of the hub-based exploration from the original Amnesia, instead you merely proceed down a linear path, occasionally stopping to complete one of the game's puzzles. The puzzles are barely worth talking about, amounting to little more than retrieving an item from six feet away and rubbing it against another item to make progress. Linearity in itself isn't a bad thing, but Frictional's previous work has generally been built around a certain degree of exploration and player freedom, both of which A Machine for Pigs severely lacks.
These changes may largely be due to different creative visions between Frictional and The Chinese Room (who developed the new Amnesia). Frictional generally tries to create games where the player's actions were directly intertwined with the story, whereas The Chinese Room instead forces players into a specific set of actions lest the player ruin the pacing of the plot. Interactivity is the key storytelling strength this medium has over films & books, something that Amnesia: A Machine for Pigs seems to forget. Players should experience your story, not merely observe it.
I may write a full review once I've finished the game, needless to say my impressions of A Machine for Pigs so far are not favourable.