After hearing many complaints of the lack of long-form games, I was shocked at the size and quality of this game. There is no need to complain!
Lydia's Heart is indeed a serious game, and it never breaks into wisecracks or in-jokes. But there is plenty that made me smile. The characters are vivid. Some are intensely likeable, some are thrillingly evil, and many, though pathetic and shallow at first glance, turn out to be complex and tragic in moving ways. Even their non-responses in conversation are interesting and revealing much of the time, though over the course of the extensive gameplay you will see a lot of repetition. Curiously, the main antagonist of the story is the least engaging, and I found his limited repertoire of remarks out of place with his much livelier associates.
At some point the game shifted from an "unfolding horror" to a puzzlefest. There are a couple mazes (not too big or nasty, but probably tedious for hardcore maze-haters), and lots of intricate puzzles. As the possiblilities spread out, the urgency of the plot faded. The satisfaction of solving a tough puzzle, or the curiosity to explore an environment, conflicted with the PC's feelings of terror and revulsion. Towards the end of the game, however, I felt more in line with the PC and her ally, and the excitement of the main goal returned.
The game takes place over the course of an afternoon. Time doesn't advance until you solve the necessary puzzles, but unlike in Ballyhoo, this trick works well because you hardly ever need to backtrack. You're told up-front that it's very hard to get permanently stuck, and there's lots of warning when you do (and all that's required in that case is an undo). Toward the end of the game I did find myself backtracking to make sure I didn't miss anything, but it almost always turned out to be unneccessary.
This is the first game I've played in a while where I deliberately avoided hints. It made the experience rich and satisfying, though the couple puzzles where I had to look up a hint (or contact the author) felt all the more unfair because of it. Even so, those puzzles made sense in retrospect.
This is a revised version of Aikin's game "Last Resort," and some of the added material is not as well fleshed-out as the rest of the game. Toward the end of the game, there were too many default responses to my attempts to solve the puzzles, even solutions I could not imagine would fail in the game-world presented. But I get the impression that there are more revisions to come, and I look forward to that.
Although I liked the flow of story overall, there were occasions when Lydia's Heart got wordy. The "death" sequence can come rather unexpectedly, and it's always the same, and covers two or three pages. It's usually possible to recover with an undo, though. The victory sequence was similarly long. I'm told that the final text-dump replaced a maze and some awkward game-states, but I would have liked to be more involved in the final scene, given a chance to savor the end of a very long journey.
I highly recommend this game. It will give you a good month of satisfying play, and you'll be glad to get to know the deceptively strong characters. I haven't played some of the "greats" of modern IF, but this is near the top of my all-time favorite list.