I don't have an issue with the new layout, rather indifferent actually. It does look like iPad based mail. But I think it really depends on how you use Mail.
For me, I always like the list of folders to show up, even if I never actually go into them. This is because it's natural for me to see the folder list; all webmail apps that I've ever used have shown them, and Outlook does as well. So hiding it by default was a little annoying, showing them again put me back at ease.
"Smart Names" or whatever is also troublesome, I made sure to disable that when I first loaded it. I like to see name and email because unfortunately, if you just show names, you can't really tell whether it's a valid sender or not. It might say "Chase Online" but really be coming from some guy in Africa.
Lastly, I like to see all recipients, To/CC, without having to request that info. So I enabled that.
Ultimately, it's mail. Doesn't have to be fancy. For times when I need more out of it I'll just go to Gmail until they bring back offline Gmail.