I agree with a lot of what you said muscle23ftl, but I have to agree with lsinger2 on one point.
Marin's portrayal of Diana is drastically different from that of Alice Ripley (and Amy Spanger at NYMF). Somehow, it seems more subdued, more human. There are many subtleties in her delivery of lines, her expressions, and her phrasing that make this character seem that much more real to me. It's not as intense of a portrayal as Alice's. It's different, but I won't say it's better. I love all three Diana's I've seen, and the way they have played the role.
I had to let Jason grow on me as Dan. I felt he was a little too theatrical in his performance of Just Another Day, but mellowed after that. I will say that I noticed expression and emotion in his portrayal (particularly when Diana in therapy) that I never saw from Joe Cassidy, Brian or Bobby.
I also notices moments between the two that I never saw from any other paring, probably coming from the fact that they know each other so well as a married couple.
I honestly couldn't discern a huge difference between Aaron and Kyle's Gabe, or Jennifer and Megahn's Natalie. If you close your eyes, you almost couldn't tell the difference between the two Gabes (besides that new crazy high note at the end of Kyle's I'm Alive). You could look right at Megahn for the whole show and not see a huge difference between her and Jennifer.
I am really impressed at how great Louis and Adam still are, despite all the turnover. You'd never know that Adam has been doing this show for 2 1/2 years and Louis for nearly 2. Their performances are still fresh and engaging. They fit perfectly with the new cast members.
I won't get into the Marin/Bernadette argument, but I will say this; if Marin had opened this show last year, I believe she would have won the Tony.
Drench yourself in words unspoken. Live your life with arms wide open. Today is where your book begins. The rest is still unwritten.
"Unwritten" Natasha Bedingfield