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.