I have to emphatically disagree. I enjoyed this game a great deal, and I intend to coax others into playing it. Maybe I didn't have the same expectations as others since I almost never pay full price for games (though I was expecting to enjoy it) but even a lot of these criticisms levied against the game, I feel, are bunk.
A lot of what I have to say could probably be summed up with the adage, 'It's about the journey, not the destination,' but to expound on that: I take umbrage at the idea that the ending is bad just because it's open-ended. Whether or not the developer ever intends to release a sequel, the player is left at the end of the game with the opportunity to imagine the duo's future adventure(s). Everything that the two have been through up until that point helps shape the perspective of those future events. It's disheartening to me that people feel the need to be spoon-fed ideas, and conclusions. Without putting words in the developer's mouth, it feels rather clear to me that the developer was giving the most blank sheet of paper he could conceive of for the player to draw his own conclusions with. I really want to challenge people to watch a movie like Hud with Paul Newman. I'm going to spoil one thing about it, and that is that the ending resolves nothing about the story, yet it's a film (released in 1963) that was nominated for, and won multiple Academy Awards.
I also find it disingenuous to say that Lilly and Ro are not given any character. They're both given a fair amount of character right at the first few screens. Of course, neither are quite given enough screen time to explore the breadth of their emotions, but I found a number of instances within the course of the game where Lilly's (albeit nuanced) (re)actions endeared her to me. At any rate, I will stop talking about it as if it were a masterpiece, as while I do think it's a very good game, I don't think it's quite THAT good. I'll concede that the game could have been substantially better off without the "bonus" character, but I don't find it to be particularly problematic, either.
Lastly, though, I want to touch on the game-play. I played Machinarium and this game back-to-back, and the former made me feel very similarly to how many seem to have responded to Lilly Looking Through: The visuals and music are outstanding, but the game-play is excruciatingly esoteric, and the final stanza is decidedly inconsequential. I don't know if anyone here feels differently about Machinarium than he does about Lilly, but Machinarium took me roughly quadruple the time investment Lilly required, and I found that the entirety of the discrepancy in time consisted of hair-pulling frustration. Even the mechanism for relieving that frustration (which I'm convinced is an essential game mechanic) is frustrating. By contrast, I found the puzzles in Lilly Looking Through to be quite intuitive. It may have taken a few clicks to figure out the exact functions of a few things, but I found everything to be clearly represented, and fairly well denoted, without anything appearing obstinately obfuscated. Indeed, the player even has help a click away to render all click-able objects apparent, should it be needed.
In the end, I enjoyed Lilly's "journey." It was rewarding in its challenge, without being obtuse, and Lilly as a character turned my mood around, as I went in upset by the resolution and rendering of the game, thinking it was another poorly implemented Flash game like Machinarium. (I later sorted out the issues with my configuration, but not before being coerced into enjoying myself on the game's own merits.) I liked the puzzles, I liked the characters, I liked the atmosphere, and I still have the option to weave the "destination" in my mind. A recommended experience.