A great game! Solve it with no frustration or need for a walkthrough. The puzzles were logical and clear. I found a message that said "the plan__sector 9" but I don't know what to do with it. I also have a valve made of sticks from the 7th zone that I didn't find a use for (doesn't seem necessary to finish the game). After finishing the game I quickly replayed to almost the end to see if I can figure out what to do with this valve... still no clue.
Just one word, WOW!
I haven't gone back to see if Alexander was mentioned in any of the other games, but they are in this game and I'm guessing it's a new character. It seems he has a strong connection with and interest in Elizabeth. I base this both on what the text in some of the notes say that you find during the game, and on some of what you can read in the 5 secrets.
There are some typos in the text, nothing that makes it hard to understand though. The game is reasonably long the first time through, but once you know what to do it should take no longer than 5-10 minutes. If I were voting on this as a standalone game I'd probably dock it a half star, but judging the series as a whole it gets a 5/5 from me.
Just when you thought it couldn't get any better, it did. THe dimension hopping thing is really though out and felt natural (and not gimmecky at all).